The solver "cplex" uses CPLEX (a trademark of ILOG) to solve integer,
mixed-integer, linear programming, and quadratic problems, including
(with version 9) problems with quadratic constraints possibly
involving integer variables.  Normally cplex is invoked by AMPL's
solve command, which gives the invocation

     cplex stub -AMPL

in which stub.nl is an AMPL generic output file (possibly written
by "ampl -obstub" or "ampl -ogstub").  After solving the problem,
cplex writes a stub.sol file for use by ampl's solve and solution
commands.  When you run ampl, this all happens automatically if you
give the AMPL commands

     option solver cplex;
     solve;

You can control cplex by setting the environment variable cplex_options
appropriately (either by using ampl's option command, or by using the
shell's set and export commands before you invoke ampl).  You can put
one or more (white-space separated) phrases in $cplex_options.  A few
of the phrases are single words:

     Phrase       Meaning

     autoopt      Use CPLEX's automatic choice of optimizer (dualopt).

     baropt       Use the barrier algorithm (unless there are discrete
                  variables).

     bestbound    Return in suffix .bestbound the best known bound on
                  the objective value.  For MIP problems with a finite
                  bestnode value (see below), bestbound = bestnode.

     bestnode     For MIP problems, return the best node value in
                  suffix .bestnode of the current objective and problem.
                  For non-MIP problems, set .bestnode to Infinity for
                  minimization, -Infinity for maximization.  If CPLEX
                  has not yet found a best node value for a MIP problem,
                  or has completely solved the problem, it similarly
                  supplies 1e75 or -1e75 as the best node value.

     concurrentopt
                  When hardware and licensing permit, try several methods in
                  parallel (with CPLEX versions >= 8).

     dual         Solve the dual problem.

     dualopt      Use a dual simplex algorithm.

     maximize     Maximize the objective, regardless of model specification.

     minimize     Minimize the objective, regardless of model specification.

     siftopt      Solve ever larger sequences of subproblems until the
                  whole LP is solved (versions of CPLEX >= 8).

     primal       Solve the primal problem (default, via "dualthresh"
                  described below).  Note that "primal", "dual", and
                  "dualthresh" determine what problem is presented to
                  CPLEX, whereas "primalopt" or "dualopt" instructs CPLEX to
                  use a primal or dual simplex algorithm, rather than making
                  an automatic choice (which currently is always "dualopt").
                  Thus "primalopt" and "dualopt" are orthogonal to "primal",
                  "dual", and "dualthresh".  The best settings depend on
                  the problem.

     primalopt    Use a primal simplex algorithm.

     relax        Ignore integrality: treat integer variables as continuous.
     version      Show the current version.

Others are name-value pairs, possibly separated by '=', as in

     iterations 600
or
     iterations=600
or
     iterations = 600

any of which limits cplex to 600 iterations.  The following names may
occur in name-value pairs.  For convenience, the list also repeats the
above single-word phrases, denoting them with "Single-word phrase".

     Name               Comment

     absmipgap          Absolute mixed-integer optimality gap tolerance
                        (for difference between current best integer solution
                        and optimal value of LP relaxation).  Default 0.

     advance            Whether to use advance basis information (initial
                        primal and dual variable values and basis indicators).
                        Default 1 (yes).

     aggcutlim          Bound on the number of constraints aggregated to
                        generate flow-cover and mixed-integer-rounding cuts;
                        default = 3.

     aggfill            Synonym for "agglim".

     aggregate          0 or 1 (default 1): Whether to make substitutions
                        to reduce the number of rows.

     agglim             Variables that appear in more than agglim rows
                        (default 10) will not be substituted away by the
                        "aggregate" algorithm.

     aggtol             Pivot tolerance for aggregating.  It seldom needs
                        fiddling.  Default = .05; must be in [1e-10, .99].

     autoopt            Single-word phrase:  use CPLEX's automatic choice of
                        optimizer (currently dualopt for LPs).

     autopt             Synonym for "autoopt".

     backtrack          Tolerance (> 0, default 0.85) for when to backtrack
                        during branch & bound.  Low values tend to pure
                        best-bound search.  High values (> 1) tend to pure
                        depth-first search.  Values less than the default
                        are often good when subproblems are expensive.

     baralg             How to start the barrier algorithm:
                                0 (default) = 1 for MIP subproblems, else 3
                                1 = infeasibility-estimate start
                                2 = infeasibility-constant start
                                3 = standard start

     barcorr            Limit on centering corrections in each iteration
                        of the barrier algorithm:
                                -1 = decide automatically (default)
                                nonnegative = at most that many

     bardisplay         Specifies how much the barrier algorithm chatters:
                                0 = no output (default)
                                1 = one line per iteration
                                2 = more output

     bargrowth          Tolerance for detecting unbounded faces in the
                        barrier algorithm: higher values make the test
                        for unbounded faces harder to satisfy.
                        Default = 1e6.

     bariterlim         Maximum barrier iterations allowed (default 200).

     barobjrange        Limit on the absolute objective value before the
                        barrier algorithm considers the problem unbounded.
                        Default = 1e15.

     baropt             Single-word phrase:  use the barrier algorithm
                        (unless there are discrete variables).

     barstart           Barrier starting-point algorithm:
                                1 = dual is 0 (default)
                                2 = estimate dual
                                3 = average of primal estimate, 0 dual
                                4 = average of primal and dual estimates

     barstartalg        Synonym for "barstart".

     baroutofcore       New in CPLEX 7.1:  whether the barrier solver should
                        use disk (out-of-core) storage for Cholesky factors:
                                0 = no (default)
                                1 = yes.
                        Withdrawn in CPLEX 10.0.

     barthreads         Maximum threads for the barrier algorithm
                        (1 unless you have a CPLEX license for multiple
                        threads).

     barvarup           Upper bound imposed by barrier algorithm on
                        variables with infinite upper bound; used to
                        prevent trouble with problems having unbounded
                        optimal faces.  Default = 1e20.
                        Withdrawn from CPLEX 9.0.

     basis_cond         Whether to show the condition number of the simplex
                        basis in the solve_message and to return its value
                        in the problem.basis_cond and objective.basis_cond
                        suffixes.  (Default = 0 = no; 1 = yes).

     basisinterval      Number of interations between savings of current
                        simplex basis to a file.  Default = 50000.
                        Deprecated in 10.0.

     bbinterval         For nodeselect = 2, select the best-bound node,
                        rather than the best-estimate node, every
                        bbinterval iterations (default 7); 0 means
                        always use the best-estimate node.

     bestbound          Single-word phrase requesting return of .bestbound
                        suffix.  See the description above.

     bestnode           Single-word phrase requesting return of .bestnode
                        suffix.  See the description above.

     boundstr           Whether to use bound strengthening in solving MIPs:
                                -1 (default) = automatic choice
                                0 = never
                                1 = always

     branch             Branching direction for integer variables:
                       -1 = down, 0 = algorithm decides, 1 = up;
                        default = 0.

     branchdir          Synonym for "branch".

     cliquecuts         Synonym for "cliques".

     cliques            Whether to use clique cuts in solving MIPs:
                                -1 = never
                                0 = automatic choice (default)
                                1 = at root node only
                                2 = at all nodes

     clocktype          Kind of times CPLEX reports during the solution
                        process:
                                1 = CPU time (default)
                                2 = wall clock time (total elapsed time)

     coeffreduce        Whether to use coefficient reduction when
                        preprocessing MIPS:
                                0 = no
                                1 = yes (default)

     comptol            Convergence tolerance for barrier algorithm:
                        the algorithm stops when the relative
                        complementarity is < bartol (default 1e-8).


     concurrentopt      Single-word phrase:  with CPLEX versions >= 8
                        and when hardware and licensing permit, try
                        several methods in parallel.

     conflictdisplay    New in CPLEX 10.0.  What to report when the
                        conflict finder is working:
                                0 = nothing
                                1 = summary (default)
                                2 = detailed display

     covercuts          Synonym for "covers".

     covers             Whether to use cover cuts in solving MIPs:
                                -1 = never
                                0 = automatic choice (default)
                                1 = at root node only
                                2 = at all nodes

     crash              Crash strategy (used to obtain starting basis);
                        possible values = -1, 0, 1; default = 1.
                        The best setting is problem-dependent and
                        can only be found by experimentation.
                        0 completely ignores the objective.

     crossover          Causes the barrier algorithm to be run (in the
                        absence of discrete variables) and specifies
                        whether to "crossover" to an optimal simplex
                        basis afterwards:
                                0 = no crossover
                                1 = crossover with primal simplex
                                    (default for baropt)
                                2 = crossover with dual simplex

     cutpass            Number of passes permitted when generating MIP
                        cutting plane:
                                -1 = none
                                 0 = automatic choice (default)
                                 positive = at most that many passes

     cutsfactor         Limit MIP cuts added to (cutsfactor-1)*m, where m
                        is the original number of rows (after presolve).
                        Default = 4.

     dgradient          Pricing algorithm for dual simplex (default 0):
                                0 = choose automatically
                                1 = standard dual pricing
                                2 = steepest-edge pricing
                                3 = steepest-edge pricing in slack space
                                4 = steepest-edge with unit initial norms.

     dense              Synonym for "densecol".

     densecol           If positive, minimum nonzeros in a column for
                        the barrier algorithm to consider the column dense.
                        If 0 (default), this tolerance is selected
                        automatically.

     dependency         Whether to use CPLEX's presolve dependency
                        checker:
                                0 = no (default)
                                1 = yes

     disjcuts           Whether to generate MIP disjunctive cuts:
                                -1 = no
                                 0 = automatic choice (default)
                                 1, 2, 3 = ever more aggressive generation

     display            Frequency of displaying LP progress information:
                        0 (default) = never; 1 = each factorization;
                        2 = each iteration.

     doperturb          1 means initially perturb the problem (by an
                        amount governed by "perturbation", which is
                        described below).  0 (default) means let the
                        algorithm decide.  Setting doperturb to 1
                        is occasionally helpful for highly degenerate
                        problems.

     dual               Single-word phrase:  solve the dual problem.

     dualopt            Single-word phrase:  use a dual simplex algorithm.

     dualthresh         Let m = number of rows, n = number of columns;
                        if m - n > dualthresh, solve the dual;
                        default = 32000.

     endbasis           "endbasis foo" writes the final basis to
                        file "foo" (in BAS format).

     endtree            File for writing final branch & bound search tree.
                        Withdrawn from CPLEX 10.

     endvector          File for writing solution from barrier algorithm
                        without crossover:  only meaningful with
                        "baropt crossover=0".

     feasibility        Amount by which basic variables can violate
                        their bounds.  Default = 1e-6; possible
                        values are between 1e-9 and 1e-4.

     feasopt            New in CPLEX 10.0.  For infeasible problems,
                        whether to find a feasible point for a relaxed
                        problem (see feasoptobj):
                                0 = no (default)
                                1 = find a feasible point
                                2 = find a "best" feasible point

     feasoptobj         New in CPLEX 10.0.  Objective for "feasopt":
                                1 = minimize sum of constraint and variable
                                        bound relaxations
                                2 = minimize number of constraint and variable
                                        bounds relaxed (a MIP problem,
                                        generally harder than feasoptobj = 1)
                                3 = minimize sum of squares of constraint and
                                        variable bound relaxations

     file               Synonym for "writeprob".

     finalfactor        Whether to factor the basis after "uncrushing"
                        the problem at the end.
                                0 = no
                                1 = yes (default)
                        Withdrawn in CPLEX 10.0.

     flowcuts           Whether to use flow cuts in solving MIPs:
                                -1 = never
                                0 = automatic choice (default)
                                1 = at root node only
                                2 = at all nodes

     flowpathcuts       Whether to generate MIP flow-path cuts:
                                -1 = no
                                 0 = automatic choice (default)
                                 1 = moderate generation
                                 2 = aggressive generation

     fraccand           Limit on number of candidate variables when
                        generating Gomory cuts for MIP problems:
                                default = 200

     fraccuts           Whether to generate MIP fractional Gomory
                        cuts:
                                -1 = no
                                 0 = decide automatically (default)
                                 1 = generate moderately
                                 2 = generate aggressively

     fracpass           Limit on number of passes to generate MIP
                        fractional Gomory cuts:
                                0 = automatic choice (default)
                                positive = at most that many passes

     fractionalcuts     Synonym for "fracpass".

     growth             Synonym for "bargrowth".

     gubcuts            Whether to use GUB cuts in solving MIPs:
                                -1 = never
                                0 = automatic choice (default)
                                1 = at root node only
                                2 = at all nodes

     heurfreq           Withdrawn from CPLEX 9.0.  How often to apply
                        "node heuristics" for MIPS:
                                -1 = never
                                0 = automatic choice (default)
                                n > 0 = every n nodes

     heuristic          Deprecated:  withdrawn from CPLEX 9.0.
                        What heuristic to use on MIPS for finding an
                        initial integer solution:
                                -1 = none
                                 0 = decide automatically (default)
                                 1 = use a rounding heuristic at node 0

     heuristicfreq      Synonym for "heurfreq".

     iisfind            Whether to find and return an IIS (irreducible
                        infeasible set of variables and constraints) if
                        the problem is infeasible:
                                0 = no (default)
                                1 = find an IIS quickly
                                2 = try to find a small IIS.
                        IIS details are returned in suffix .iis, which
                        assumes one of the values "non" for variables
                        and constraints not in the IIS; "low" for
                        variables or inequality constraint bodies whose lower
                        bounds are in the IIS; "upp" for variables and
                        inequality constraint bodies whose upper bounds are
                        in the IIS; and "fix" for equality constraints that
                        are in the IIS.

     impliedcuts                Whether to use implied cuts in solving MIPs:
                                -1 = never
                                0 = automatic choice (default)
                                1 = at root node only
                                2 = at all nodes

     integrality        Amount by which an integer variable can differ
                        from the nearest integer and still be considered
                        feasible.  Default = 1e-5; must be >= 1e-9.

     intwarntol         Do not warn about perturbations to "integer"
                        variables to make them integers when the maximum
                        perturburation is at most intwarntol (default 1e-9);
                        see "round".

     iterations         Limit on total LP iterations; default 5000000.

     iterlim            Synonym for "iterations".

     limitperturb       Synonym for "perturblimit".

     lazy               Whether to recognize suffix .lazy on constraints
                        (new for CPLEX 10): sum of
                                1 ==> treat .lazy = 1 as lazy constraint
                                2 ==> treat .lazy = 2 as user cut
                        Default lazy = 3 ==> treat both.  (Suffix .lazy on
                        constraints is ignored if not 0, 1, or 2 modulo 3.)

     lbheur             Whether to use a local branching heuristic in an
                        attempt to improve new incumbents found during a
                        MIP search.  (Default = 0 = no; 1 = yes.)

     logfile            Name of file to receive all CPLEX messages.

     lowercutoff        For maximization problems involving integer
                        variables, skip any branch whose LP relaxation's
                        optimal value is less than lowercutoff.  Warning:
                        if lowercutoff is too large, the problem will
                        appear infeasible.  Default = -Infinity.

     lowerobj           Stop minimizing when the objective value
                        goes below lowerobj.  Default = -1e75.

     lowerobjlim        Synonym for "lowerobj".

     lpdisplay          Synonym for "display".

     lpiterlim          Synonym for "iterations".

     lptimelim          Synonym for "time".

     markowitz          Pivot tolerance; default = 0.01; must be between
                        0.0001 and 0.99999.  Bigger values may improve
                        numerical properties of the solution (and may
                        take more time).

     maximize           Single-word phrase:  maximize the objective,
                        regardless of model specifications.

     memoryemphasis     New in CPLEX 10.0.  Whether to compress data to reduce
                        the memory used, which may make some information (e.g.,
                        basis condition) unavailable:
                                0 = no (default)
                                1 = yes

     minimize           Single-word phrase:  minimize the objective,
                        regardless of model specifications.

     mipalg             Algorithm used on mixed-integer subproblems
                        (default 2):
                                1 = primal simplex
                                2 = dual simplex (plus primal, if dual fails)
                                3 = network alg., then dual simplex
                                4 = barrier with crossover
                        The next two are not available in CPLEX versions >= 8;
                        specify mipcrossover instead.
                                5 = dual to iteration limit, then barrier
                                6 = barrier without crossover

     mipalgorithm       Synonym for "mipalg".

     mipbasis           Whether to compute a basis and dual variables for MIP
                        problems when endbasis is not specified:
                                0 = no
                                1 = yes (default)
                        This keyword is new with driver version 20040716.
                        When endbasis is specified, mipbasis=1 is assumed.
                        Otherwise, when mipbasis=0 is specified for a MIP
                        problem, no solver-status values for variables are
                        returned to AMPL.

     mipcrossover       Crossover method used when using the barrier
                        method for MIP subproblems:
                                -1 = no crossover
                                 0 (default) = automatic choice
                                 1 = primal
                                 2 = dual

     mipcuts            Sets all nine of cliques, covers, disjcuts,
                        flowcuts, flowpathcuts, fraccuts, gubcuts,
                        impliedcuts and mircuts to the specified value.

     mipdisplay         Frequency of displaying branch-and-bound
                        information (for optimizing integer variables):
                                0 (default) = never
                                1 = each integer feasible solution
                                2 = every "mipinterval" nodes
                                3 = every "mipinterval" nodes plus
                                    information on LP relaxations
                                    (as controlled by "display")
                                4 = same as 2, plus LP relaxation info.
                                5 = same as 2, plus LP subproblem info.

     mipemphasis        Whether to emphasize seeking optimality (0 =
                        default) or finding feasible solutions (1).
                        For CPLEX versions >= 8, two other values are
                        possible:  emphasizing optimality over
                        feasibility (2) and emphasizing best bound (3).

     mipgap             Relative tolerance for optimizing integer
                        variables: stop if
                              abs((best bound) - (best integer))
                                  < mipgap * (1 + abs(best bound)).
                        Default = 1e-4; must be between 1e-9 and 1.

     mipinterval        Frequency of node logging for mipdisplay 2 or 3.
                        Default = 1.

     mipordertype       Synonym for "ordertype".

     mipsolutions       Stop branch-and-bound for integer variables
                        after finding "mipsolutions" feasible solutions.
                        Default = 2100000000.

     mipstart           Synonym for "mipstartvalue".

     mipstartalg        Which LP algorithm to use in solving the initial
                        MIP subproblem:
                                1 = primal simplex
                                2 = dual simplex (default)
                                3 = netopt
                                4 = barrier with crossover
                        The next two are not available in CPLEX versions >= 8;
                        specify mipcrossover instead.
                                5 = dual simplex to iteration limit,
                                    then barrier
                                6 = barrier without crossover

     mipstartstatus     Whether to use incoming variable and constraint
                        statuses if the problem has integer variables:
                                0 = no
                                1 = yes (default).

     mipstartvalue      Whether to use initial guesses in problems with
                        integer variables:
                                0 = no
                                1 = yes (default).

     mipsubalg          Synonym for "mipalg".

     mipthreads         Maximum threads for the MIP algorithm
                        (1 unless you have a CPLEX license for multiple
                        threads).

     mircuts            Whether to generate MIP rounding cuts:
                                -1 = no
                                 0 = automatic choice (default)
                                 1 = moderate generation
                                 2 = aggressive generation

     nameround          Whether to mangle variable and constraint names
                        by turning [ and ] into ( and ), respectively:
                                0 = no (default)
                                1 = yes.
                        This only matters if you specify endbasis=...
                        or startbasis=... or perhaps writeprob=something.lp
                        and have instructed AMPL to write .row and .col files.
                        (It is usually better to let AMPL's status facilities
                        convey basis information.)  An alternative under Unix
                        is to use the "tr" command to make the above changes
                        if they are needed.

     netdisplay         Which objective value to show when using the
                        network simplex algorithm with display > 0:
                                0 = none
                                1 = true objective
                                2 = penalized objective (default)

     netfeasibility     Feasibility tolerance for the network simplex
                        algorithm.  Default = 1e-6; possible values are
                        between 1e-11 and 1e-1.

     netfind            Algorithm for finding embedded networks:
                                1 = extract only the natural network (default)
                                2 = use reflection scaling
                                3 = use general scaling

     netfinder          Synonym for "netfind".

     netiterations      Limit on network simplex iterations.
                        Default = large (e.g., 2100000000).

     netopt             0 means never invoke the network optimizer.
                        1 (default) means invoke the network optimizer
                          only if the model had node and arc declarations.
                        2 means always invoke the network optimizer
                          (unless there are integer variables); the network
                          optimizer may be able to find and exploit an
                          embedded network.

     netoptimality      Tolerance for optimality of reduced costs in the
                        network simplex algorithm.  Default 1e-6; must be
                        between 1e-11 and 1e-1.

     netpricing         How to price in the network simplex algorithm:
                                0 = automatic choice (default)
                                1 = partial pricing
                                2 = multiple partial pricing
                                3 = multiple partial pricing with sorting

     node               Synonym for "nodes".

     nodefile           Whether to save node information in a temporary file:
                                0 = no
                                1 (default) = compressed node file in memory
                                2 = node file on disk
                                3 = compressed node file on disk.

     nodefiledir        Synonym for workfiledir.  Prior to CPLEX 7.1,
                        this directory is just for node information files.

     nodefilelim        Maximum size for the node file.  Default 1e75.
                        Removed from CPLEX 7.1.  See workfilelim.

     nodefilesize       Synonym for "nodefilelim".

     nodelim            Synonym for "nodes".

     nodes              Stop branch-and-bound for integer variables
                        after "nodes" LP relaxations.  Default = 2100000000.

     nodesel            Strategy for choosing next node while optimizing
                        integer variables:
                          0 = depth-first search;
                          1 = breadth-first search (default);
                          2 = best-estimate search;
                          3 = alternate best-estimate search.

     nodeselect         Synonym for "nodesel".

     numericalemphasis  New in CPLEX 10.0.  Whether to try to improve
                        numerical accuracy (at a possible cost of time or
                        memory):
                                0 = no (default)
                                1 = yes

     objdifference      Amount added to (for maximizing) or subtracted
                        from (for minimizing) the best (so far) feasible
                        objective value while optimizing integer variables.
                        Subsequent nodes will be ignored if their LP
                        relaxations have optimal values worse than this
                        sum.  Default = 0.  Positive values may speed
                        the search -- and may cause the optimal solution
                        to be missed.

     objno              0 (default) = first objective, 1 = second, etc.
                        This only matters if you declare several
                        objectives and do not use AMPL's drop or objective
                        commands to select a single objective for the solver
                        (CPLEX) to see.

     optimality         Tolerance for optimality of reduced costs.
                        Default 1e-6; must be between 1e-9 and 1e-1.

     optimize           Synonym for "primal".

     ordering           Ordering algorithm used by the barrier algorithm
                        0 = automatic choice (default)
                        1 = approximate minimum degree
                        2 = approximate minimum fill
                        3 = nested disection.

     ordertype          How to generate default priorities for integer
                        variables when no .priority suffix is specified:
                                0 = do not generate priorities (default)
                                1 = use decreasing costs
                                2 = use increasing bound range
                                3 = use coefficient count.

     outlev             Synonym for "display".

     pdswitch           Whether to switch algorithms (from primal to dual
                        or vice versa) when undoing perturbations or shifts
                        made during the primal or dual simplex algorithm:
                                -1 = no
                                 0 = automatic choice (default)
                                 1 = yes
                        pdswitch=1 may help if there are many cycles
                        of undoing perturbations.  New in CPLEX 7.0,
                        hidden in CPLEX 7.1.

     perturb            Synonym for "doperturb".

     perturbation       Amount by which to perturb variable bounds
                        when perturbing problems (see "doperturb").
                        Default 1e-6; must be positive.

     perturbconst       Synonym for "perturbation".

     perturblim         Number of stalled simplex iterations before the
                        problem is perturbed.  Default = 0 = automatic.

     perturblimit       Synonym for "perturblim".

     pgradient          Pricing algorithm for primal simplex (default 0):
                                -1 = reduced-cost pricing
                                 0 = hybrid reduced-cost and Devex pricing
                                 1 = Devex pricing
                                 2 = steepest-edge pricing
                                 3 = steepest-edge with slack initial norms
                                 4 = full pricing.

     plconpri           Priority (default 1) for SOS2 constraints for nonconvex
                        piecewise-linear terms in constraints.

     plobjpri           Priority (default 2) for SOS2 constraints for nonconvex
                        piecewise-linear terms in objectives.

     polishtime         New in CPLEX 10.0:  seconds to spend "polishing" integer
                        solutions.  Default 0.

     precompress        New in CPLEX 7.1:  whether to compress the original
                        problem after CPLEX's presolve:
                                -1 = no
                                 0 = automatic choice (default)
                                 1 = yes
                        Withdrawn in CPLEX 10.0.

     predual            Whether CPLEX's presolve phase should present the
                        CPLEX solution algorithm with the primal (-1) or
                        dual (1) problem or (default = 0) should decide
                        which automatically.  Specifying "predual=1" often
                        gives better performance than specifying just "dual",
                        but sometimes "dual predual=1" is still better.

     prelinear          Whether CPLEX's presolve should do full reductions
                        or only linear ones.  Default = 1 = full.

     prereduce          Kinds of reductions permitted during CPLEX presolve:
                                0 = none
                                1 = only primal
                                2 = only dual
                                3 = both primal and dual (default)

     prerelax           Whether to use CPLEX's presolve on the initial LP
                        relaxation of a MIP:
                                0 = no (default)
                                1 = yes.

     prepass            Limit on number of CPLEX presolve passes.
                        Default = -1 = decide limit automatically.

     presolve           0 or 1 (default 1): Whether to run CPLEX's presolve
                        algorithm.

     presolvedual       Synonym for "predual".

     presolvenode       -1, 0, or 1 (default 0): Whether to run CPLEX's
                        presolve at each node of the MIP branch-and-bound
                        tree: -1 = no; 1 = yes; 0 = automatic choice.

     prestats           0 or 1 (default 0): Whether to print results of
                        and time for CPLEX's "aggregate" and "presolve"
                        algorithms.

     pricing            Size of pricing candidate list (for partial pricing).
                        0 (default) means the algorithm decides.

     primal             Single-word phrase:  solve the primal problem.

     primalopt          Use the primal simplex algorithm.

     priorities         Whether to consider priorities for MIP branching:
                                0 = no
                                1 = yes (default)

     probe              Whether to do variable probing when solving MIPs
                        (which sometimes dramatically affects performance,
                        for better or worse):
                                -1 = no
                                0 = automatic choice (default)
                                1, 2, or 3 = ever more probing.

     probetime          New in CPLEX 10.0.  Limit in seconds on time spent
                        probing.  Default = 1e75.

     qcpconvergetol     Convergence tolerance on relative complementarity for
                        problems with quadratic constraints.  Default = 1e-6.

     rays               Whether to return suffix .unbdd when the objective is
                        unbounded or suffix .dunbdd when the constraints are
                        infeasible:
                                0 = neither
                                1 = just .unbdd
                                2 = just .dunbdd
                                3 = both (default)

     readbasis          BAS file containing starting basis.

     readvector         VEC file containing starting point for barrier alg.

     refactor           LP iterations between refactorizing the basis.
                        0 (default) means the algorithm decides.

     relax              Single-word phrase:  ignore integrality.

     relaxpresolve      Synonym for "prerelax".

     relobjdif          Synonym for "relobjdiff".

     relobjdiff         If the objdifference parameter is 0,
                        relobjdiff times the absolute value of the objective
                        value is added to (for maximizing) or subtracted
                        from (for minimizing) the best (so far) feasible
                        objective value while optimizing integer variables.
                        Subsequent nodes will be ignored if their LP
                        relaxations have optimal values worse than this
                        sum.  Default = 0.  Positive values may speed
                        the search -- and may cause the optimal solution
                        to be missed.

     repairtries        New in CPLEX 10.0.  How many times to try to
                        repair in infeasible MIP starting guess:
                                 -1 = none
                                  0 = automatic choice (default)
                                > 0 = that many times

     repeatpresolve     New in CPLEX 10.0.  Whether to repeat CPLEX's
                        presolve at MIP nodes:
                                -1 = automatic choice (default)
                                 0 = no
                                 1 = presolve again ignoring cuts
                                 2 = presolve again considering cuts
                                 3 = presolve again considering cuts and
                                        allowing new root cuts

     return_mipgap      Whether to return mipgap suffixes or include
                        mipgap values in the solve_message:  sum of

                                 1 = return relmapgap suffix
                                 2 = return absmipgap suffix
                                 4 = suppress mipgap values in solve_message

                        The suffixes are on the objective and problem;
                        returned suffix values are +Infinity if no integer-
                        feasible solution has been found, in which case no
                        mipgap values are reported in the solve_message.
                        Default = 0.  See also bestbound and bestnode above.

     rinsheur           Relaxation INduced neighborhood Search HEURistic
                        for MIP problems:
                                -1 = none
                                 0 = automatic choice of interval (default)
                                 n (for n > 0) = every n nodes.

     relpresolve        Synonym for "prerelax".

     rootheuristic      Withdrawn from CPLEX 9.0.  Synonym for "heuristic".

     round              Whether to round integer variables to integral
                        values before returning the solution, and whether
                        to report that CPLEX returned noninteger values
                        for integer values (default 1):  sum of
                                1 ==> round nonintegral integer variables
                                2 ==> do not modify solve_result
                                4 ==> do not modify solve_message
                                8 ==> modify solve_result and solve_message
                        even if maxerr < intwarntol (default 1e-9).
                        Modifications take place only if CPLEX assigned
                        nonintegral values to one or more integer variables.

     scale              How to scale the problem:
                        -1 = no scaling
                        0 (default) = equilibration
                        1 = a more aggressive scheme that sometimes helps.

     sensitivity        Whether to return sensitivy information for the
                        objective (in suffixes .up for the largest value
                        of a variable's cost coefficient or constraint's
                        right-hand side before the optimal basis changes,
                        .down for the smallest such value, and .current for
                        the current cost coefficient or right-hand side):
                                0 = no (default)
                                1 = yes.

     siftingopt         Synonym for "siftopt".

     siftopt            Single-word phrase:  on LPs with CPLEX versions >= 8,
                        solve ever larger sequences of subproblems until the
                        whole LP is solved.

     simthreads         Maximum threads for the dual simplex algorithm
                        (currently always 1).  Withdrawn from CPLEX 9.0.

     singular           Maximum number of times CPLEX should try to
                        repair the basis when it encounters singularities.
                        Default = 10.

     singularlim        Synonym for "singular".

     solutionlim        Synonym for "mipsolutions".

     sos                0 or 1 (default 1):  Whether to honor declared
                        suffixes .sosno and .ref describing SOS sets.
                        Each distinct nonzero .sosno value designates an SOS
                        set, of type 1 for positive .sosno values and of type
                        2 for negative values.  The .ref suffix contains
                        corresponding reference values.

     sos2               0 or 1 (default 1): Whether to tell CPLEX about SOS2
                        constraints for nonconvex piecewise-linear terms.

     startalg           Synonym for "mipstartalg".

     startalgorithm     Synonym for "mipstartalg".

     startbasis         "startbasis foo" reads the initial basis
                        (in BAS format) from file "foo".

     starttree          File for reading initial branch-and-bound search tree.
                        Withdrawn from CPLEX 10.

     strongcand         Length of the candidate list for "strong branching"
                        when solving MIPs: default 10.

     strongit           Number of simplex iterations on each variable in
                        the candidate list during strong branching.
                        Default = 0 = automatic choice.

     strongthreads      Maximum threads during strong branching.
                        Default = 1.

     subalg             Synonym for "mipalg".

     subalgorithm       Synonym for "mipalg".

     submipnodelim      Limit on nodes searched by relaxation induced
                        neighborhood search (RINS) heuristic for MIP
                        problems.  Default = 500.

     symmetry           New in CPLEX 9.1?  Whether to break symmetry during
                        preprocessing of MIP problems:
                                -1 = automatic choice (default)
                                 0 = no
                                 1 = moderate effort
                                 2 = more effort
                                 3 = still more effort

     threads            Default maximum number of threads for any of
                        the parallel CPLEX optimizers (limited also
                        by licensing).  Default = 1.  May be overridden
                        by more specific limits, such as barthreads or
                        mipthreads.

     time               Time limit in seconds; default = 1e75.

     timelimit          Synonym for "time".

     timing             1 means write time to stdout, 2 to stderr,
                        3 to both stdout and stderr, 0 to neither.
                        Default = 0.

     tranopt            Synonym for "dualopt".

     treelimit          Synonym for "treememory".

     treememlim         Synonym for "treememory".

     treememory         Max. megabytes of memory (default 128) to use for
                        branch-and-bound tree.

     uppercutoff        For minimization problems involving integer
                        variables, skip any branch whose LP relaxation's
                        optimal value is more than uppercutoff.  Warning:
                        if uppercutoff is too small, the problem will
                        appear infeasible.  Default = Infinity.

     upperobj           Stop maximizing when the objective value
                        goes above upperobj.  Default = 1e75.

     upperobjlim        Synonym for "upperobj".

     varsel             Strategy for selecting the next branching
                        variable during integer branch-and-bound:
                        -1 = branch on variable with smallest
                             integer infeasibility;
                         0 = algorithm decides (default);
                         1 = branch on variable with largest
                             integer infeasibility;
                         2 = branch based on pseudo costs (new in CPLEX 6.5);
                         3 = strong branching;
                         4 = branch based on pseudo reduced costs
                             (with CPLEX 6.5; varsel 2 had this meaning
                             with earlier versions of CPLEX).

     varselect          Synonym for "varsel".

     version            Single-word phrase:  show the current version.

     wantsol            In a stand-alone invocation (no -AMPL on the
                        command line), what solution information to write.
                        Sum of
                                1 = write .sol file
                                2 = primal variables to stdout
                                4 = dual variables to stdout
                                8 = suppress solution message

     workfiledir        Directory where CPLEX creates a temporary
                        subdirectory for temporary files, e.g., for
                        node information and Cholesky factors.

     workfilelim        Maximum size in megabytes for in-core work "files".
                        Default 128.

     writebas           Synonym for "endbasis".

     writeprob          Name of file to which the problem is written
                        in a format determined by the name's suffix:
                                .sav = binary SAV file;
                                .mps = MPS file, original names;
                                .lp = LP file, original names;
                                .rmp = MPS file, generic names;
                                .rew = MPS file, generic names;
                                .rlp = LP file, generic names.
                        SAV and LP formats are peculiar to CPLEX.

     writevector        Synonym for "endvector".

     xxxstart           Whether to read .xxx files to resume an
                        interrupted run of CPLEX (deprecated in 10.0):
                                0 = no (default)
                                1 = yes.

When CPLEX finds the problem unbounded and a basis is available,
a ray is returned in suffix unbdd.

For problems with several integer (or binary) variable declarations,
it sometimes helps to specify branching priorities for the integer
variables.  When CPLEX has a choice of which integer variable to
bound (or fix) during its branch-and-bound algorithm, it chooses
a variable with the highest priority.  You can declare suffix priority
and assign individual priorities (between 0 and 2147483647) to each
integer variable.  Assigning .priority values is the preferred
approach, but you can also use the older and less flexible scheme of
specifying priorities in the environment variable $mip_priorities,
which should contain zero or more white-space separated pairs of the
form
        variable-name priority
Each priority should be an integer between 1 and 2147483647.
All components of an indexed variable have the same priority;
the variable-name should not have a subscript.

If suffix priority is present, option mip_priorities is ignored.

You can also declare suffix direction and use it to convey
individual branching directions (-1, 0, or 1, as with the branch
keyword described above) for each integer variable.  If suffix
direction is present, the branch keyword applies only to variables
whose .direction is 0.

When using $mip_priorities, you must arrange for AMPL to write a .col
file.  See the discussion of auxiliary files on p. 333 of the AMPL book:
unless $cplex_auxfiles already contains 'c', issue the AMPL command
        option cplex_auxfiles c;
before saying "solve;".  Similarly, if you use AMPL's write command,
first make sure $auxfiles contains 'c'; if not, issue the AMPL command
        option auxfiles c;
The keywords '!quit' and '!echo' may appear at the beginning of
$mip_priorities.  If cplex finds an error in $mip_priorities, it bails
out unless '!quit' appears in $mip_priorities before the error.
Normally cplex reports the priorities it acquires from $mip_priorities,
but '!echo' suppresses this reporting.  For example, if Buy is an
integer variable, you might try the AMPL commands
        option mip_priorities 'Buy 3', cplex_auxfiles ''; solve;
        option mip_priorities '!quit Buy 3'; solve;
        option cplex_auxfiles c; solve;
        option mip_priorities '!echo Buy 3'; solve;
        option mip_priorities '!quit !echo Buy 3'; solve;

-----------------------
solve_result_num values
=======================

Here is a table of solve_result_num values that "cplex" can return
to an AMPL session, along with the text that appears in the associated
solve_message.

        Value   Message

          0     optimal solution
          1     primal has unbounded optimal face
          2     optimal integer solution
          3     optimal integer solution within mipgap or absmipgap
          4     primal optimal (no dual solution available)
        100     best solution found, primal-dual feasible
        102     optimal (non-)integer solution
        103     optimal (non-)integer solution within mipgap or absmipgap
        110     optimal with unscaled infeasibilities
        111     integer optimal with unscaled infeasibilities
        121     feasible relaxed sum in feasopt
        122     optimal relaxed sum in feasopt
        123     feasible relaxed infeasibility count in feasopt
        124     optimal relaxed infeasibility count in feasopt
        125     feasible relaxed quadratic penalty in feasopt
        126     optimal relaxed quadratic penalty in feasopt
        200     infeasible problem
        201     infeasible with phase II singularities
        202     infeasible with phase I singularities
        204     converged, dual feasible, primal infeasible
        205     converged, primal and dual infeasible
        206     best solution found, primal infeasible
        207     best solution found, primal-dual infeasible
        208     infeasible or unbounded in presolve
        209     integer infeasible or unbounded in presolve
        210     infeasible problem found by dualopt; .dunbdd returned
        220     integer infeasible
        300     unbounded problem
        301     converged, primal feasible, dual infeasible
        302     best solution found, dual infeasible
        310     unbounded problem found by primalopt; .unbdd returned
        320     integer unbounded ray
        400     objective limit exceeded in phase II
        401     iteration limit in phase II
        402     iteration limit in phase I
        403     time limit in phase II
        404     time limit in phase I
        405     primal objective limit reached
        406     dual objective limit reached
        410     node limit with no integer solution
        411     time limit with no integer solution
        412     treememory limit with no integer solution
        413     node file limit with no integer solution
        420     mixed-integer solutions limit
        421     node limit with integer solution
        422     time limit with integer solution
        423     treememory limit with integer solution
        424     node file limit with integer solution
        500     unrecoverable failure
        501     aborted in phase II
        502     aborted in phase I
        503     aborted in barrier, dual infeasible
        504     aborted in barrier, primal infeasible
        505     aborted in barrier, primal and dual infeasible
        506     aborted in barrier, primal and dual feasible
        507     aborted in crossover
        508     solution found, numerical difficulties
        509     solution found, inconsistent equations
        510     unrecoverable failure with no integer solution
        511     aborted, no integer solution
        512     out of memory, no tree; no integer solution
        520     unrecoverable failure with integer solution
        521     aborted, integer solution exists
        523     out of memory, no tree; solution may exist
        530     bug? problem has no variables
        531     bug? Error return from named CPLEX routine
        540     Diagonal QP Hessian has elements of the wrong sign
        541     QP Hessian has diag. elements of the wrong sign
        542     QP Hessian is not positive definite
        550     problem has (nonquadratic) nonlinear constraints
        551     problem has a nonlinear objective
        552     problem has nonlinear integer variables
        553     problem has integer variables and a quadratic objective
        554     problem has unlinearized piecewise-linear terms
        555     problem has a quadratic objective involving division by 0
        556     nonlinear objective without CPLEX Barrier option (for QPs)
        557     CPLEX MIP option needed to handle piecewise-linear terms
        558     quadratic constraint involves division by zero
        559     bug: no quadratic terms in "nonlinear" constraint
        560     error in $cplex_options
        561     surprise return from a CPLEX routine (perhaps a driver bug)
        562     constraint is not convex quadratic
        563     logical constraint is not an indicator constraint
        570     CPLEX licensing problem
        571     not licensed to solve MIP problems
        572     not licensed to use the barrier algorithm
        573     not licensed to solve MIQP or QCP problems


The CPLEX driver is supposed to distinguish infeasibility from unboundedness,
so solve_result_num should never be 208 or 209.  If you find an example where
one of these values does occur, please send it to us.

-------------------

If you have a CPLEX 4.0 manual, you may find the following table
helpful.  It relates the above names (in name-value pairs) to
SET commands described in chapters 8 and 9 of the CPLEX 4.0 manual.

     Name               CPLEX SET command

     agglim             PREPROCESSING colnonzeros
     bardisplay         SET BARRIER display
     bargrowth          SET BARRIER limits growth
     bariterlim         SET BARRIER limits iterations
     barobjrange        SET BARRIER limits objrange
     barthreads         SET BARRIER LIMIT THREADS
     barvarup           SET BARRIER LIMITS varupper
     branch             SET MIP STRATEGY branch
     cliques            MIP STRATEGY cliques
     coeffreduce        PREPROCESSING coeffreduce
     comptol            SET BARRIER convergetol
     covers             MIP STRATEGY covers
     crash              SET SIMPLEX crash
     dense              SET BARRIER colnonzeros
     dependency         PREPROCESSING dependency
     dgradient          SET SIMPLEX dgradient
     display            SET SIMPLEX display
     doperturb          SET SIMPLEX perturbation
     feasibility        SET SIMPLEX TOLERANCE feasibility
     heuristic          MIP STRATEGY heuristic
     integrality        SET MIP TOLERANCE integrality
     iterations         SET SIMPLEX LIMIT iterations
     iterlim            SET SIMPLEX LIMIT iterations
     lowercutoff        SET MIP STRATEGY lowercutoff
     lowerobj           SET SIMPLEX LIMIT lowerobj
     markowitz          SET SIMPLEX TOLERANCE markowitz
     mipdisplay         SET MIP display
     mipgap             SET MIP TOLERANCE mipgap
     mipinterval        SET MIP interval
     mipsolutions       SET MIP LIMIT solutions
     mipstartalg        MIP STRATEGY startalgorithm
     mipsubalg          MIP STRATEGY subalgorithm
     mipthreads         SET MIP LIMIT THREADS
     netfind            SIMPLEX netfind
     nodefile           SET MIP STRATEGY FILE
     nodes              SET MIP LIMIT nodes
     nodesel            SET MIP STRATEGY nodeselect
     objdifference      SET MIP TOLERANCE objdifference
     optimality         SET SIMPLEX TOLERANCE optimality
     ordering           SET BARRIER ordering
     outlev             SET SIMPLEX display
     perturbation       SET SIMPLEX perturbation <number>
     pgradient          SET SIMPLEX pgradient
     pricing            SET SIMPLEX pricing
     priorities         MIP STRATEGY order
     refactor           SET SIMPLEX refactor
     relobjdiff         MIP TOLERANCES relobjdifference
     scale              SET read scale
     simthreads         SET SIMPLEX LIMIT THREADS
     singular           SET SIMPLEX LIMIT singular
     sosmin             MIP LIMITS minsossize
     time               SET timelimit
     uppercutoff        SET MIP TOLERANCE uppercutoff
     upperobj           SET SIMPLEX LIMIT upperobj
     varsel             SET MIP STRATEGY variableselect

-------------------

Keywords added for CPLEX 6.5:

        barstart
        bbinterval
        boundstr
        cutsfactor
        flowcuts
        gubcuts
        heuristicfreq
        impliedcuts
        mipcrossover
        mipcuts
        nodefilelim
        ordertype
        perturblimit
        prerelax
        probe
        strongcand
        strongit
        strongthreads

Keywords no longer available in CPLEX 6.5:

     reducecostfix      Whether to use reduced cost fixing in MIP problems:
                                0 = no
                                1 = yes (default)

     sosmin             Minimum number of members in a set for the
                        set to be considered of SOS type 3.

     sosscan            0 or 1 (default 0): Whether to scan for SOS3 sets.

Keywords added for CPLEX 7.0:

        aggcutlim
        barstartalg
        cutpass
        disjcuts
        flowpathcuts
        fraccand
        fracpass
        heurfreq
        limitperturb
        mipemphasis
        mipordertype
        mipstart
        mircuts
        nodefiledir
        nodefilesize
        pdswitch
        perturblim
        prereduce
        presolvedual
        presolvenode
        relaxpresolve
        relpresolve

Keywords removed for CPLEX 7.1:

        nodefilelim
        nodefilesize

Keywords added for CPLEX 8.0 (excluding undocumented keywords,
which are discussed below):

        autoopt
        autopt
        baroutofcore
        concurrent
        concurrentopt
        precompress
        rays
        siftingopt
        siftopt
        threads
        workfilelim

Keywords added for CPLEX 9.0:

        finalfactor
        qcpconvergetol
        rinsheur
        submipnodelim

Keywords removed for CPLEX 9.0:

        barvarup
        heuristic
        rootheuristic
        simthreads

Keywords added for CPLEX 9.1:

        basis_cond
        lbheur
        prelinear
        prepass

-------------------

If you invoke "cplex stub -AMPL" or "cplex stub", you can also supply
additional command-line arguments of the form name=value.  Such
arguments override specifications in $cplex_options.  Example:

     ampl -obfoo foo.model foo.data
     nohup cplex foo timing=2 2>>times&

to solve a problem whose solution will take a while; after cplex
finishes,

     ampl foo.model foo.data -
     solution foo.sol;
     display ... /* things involving the computed solution */;

(Here, - denotes standard input, and ampl reads the "solution..."
and "display..." lines.)

When invoked with no arguments, cplex either operates as described
in the CPLEX manual (when compiled with -DStand_alone on systems
where the CPLEX callable library provides cpxmain()), or complains
about not having a stub.

-------------------

In addition to the keyword phrases described above, cplex recognizes
some directives (name-value pairs, separated by white space and/or an
= sign, appearing either in $cplex_options or on the command line) for
settings not described in the official CPLEX documentation.  These
"undocumented" directives all begin with underscore.  You are unlikely
ever to need to use them, as the default settings suffice in most
cases.  They are provided for the rare cases where CPLEX technical
support may recommend their use.  The directive names appear at the
beginning of the output you will get by invoking
        cplex "-="
(or 'cplexamp "-="' if you follow the ILOG naming practice).

*************************

If you have questions about or find bugs with this stuff,
please contact:

     David M. Gay
     dmg@ampl.com
