## GSLIB Help Page: SASIM

Description:

- `sasim` allows conditional simulations of a continuous variable honoring any combination of the following input statistics: histogram, variogram, indicator variograms, correlation coefficient with a secondary variable, or conditional distributions with a secondary variable.

Parameters:

- objhist, objvarg, objivar, objcorr, objcpdf: binary flags that specify whether or not a component objective function will be considered (set to 1 if yes, 0 if not).
- sclhist, sclvarg, sclivar, sclcorr, sclcpdf: user imposed scaling factors that will multiply the scaling factors that the program automatically calculates (see section V.6).
- ilog: if set to 1, the logarithm (base 10) of the variable will be considered. This is appropriate for positively skewed variables with large variance.
- nsim: the number of realizations to generate.
- nx, xmn, xsiz: definition of the grid system (x axis).
- ny, ymn, ysiz: definition of the grid system (y axis).
- nz, zmn, zsiz: definition of the grid system (z axis).
- seed: random number seed (a large odd integer).
- idbg: an integer debugging level between 0 and 3.
- dbgfl: the file for the debugging output.
- outfl: the output grid is written to this file. The output file will contain the results, cycling fastest on x then y then z then simulation by simulation.
- isas: the annealing schedule (next set of parameters) can be set explicitly or it can be set automatically (0=automatic,1=then use the next three lines of input).
- t0, redfac, ka, k, num, omin: the annealing schedule: initial temperature, the reduction factor, the maximum number of perturbations at any one given temperature, and the target number of acceptable perturbations at a given temperature, the stopping number (maximum number of times that the ka is reached), and a low objective function value indicating convergence.
- maxpert: the maximum number of perturbations (will be scaled by nx x ny x nz)
- report: After a fixed number of swaps (report scaled by nx x ny x nz) the objective function is written to the screen and the debugging file.
- icond: set to 1 if there is conditioning data (0 implies no conditioning data).
- condfl: an input data file with the conditioning data (simplified Geo-EAS format). If this file does not exist then an unconditional simulation is generated.
- icolx, icoly, icolz, and icolvr: the column numbers for the x,y, and z coordinates and the variable to be simulated. One or two of the coordinate column numbers can be set to zero which indicates that the simulation is 2-D or 1-D.
- tmin and tmax: all values strictly less than tmin and strictly greater than tmax are ignored.
- ihist: set to 1 if the histogram should be taken from the following file (set to 0 if not).
- histfl: an input data file with the histogram in simplified Geo-EAS format.
- icolvr, and icolwt: the column numbers for the variable to be simulated and a declustering weight.
- nquant: number of quantiles for the histogram objective function
- nivar: number of indicator variograms to consider. The threshold values (in units of the primary variable) are input next and the variograms are input directly after the direct variogram of the primary variable with the same format.
- ithreshold: The threshold values (in units of the primary variable) for the indicator variograms
- secfl: an input data file with the secondary variable model (needed if cosimulation is being performed)
- icolsec: the column number for the secondary variable in secfl
- vertavg: if set to 1, then the correlation applies to the secondary variable and a vertical average of the variable being simulated. Otherwise, the secondary variable is considered at each grid node location.
- corrcoef: The correlation coefficient (used if the fourth component objective function is turned on).
- bivfl: an input data file with the bivariate data to define the conditional distributions (simplified Geo-EAS format)
- icolpri and icolsec: the column numbers for the primary and secondary variables in bivfl
- tmin and tmax: all values strictly less than tmin and strictly greater than tmax are ignored.
- npricut: number of thresholds to define the conditional distributions of the primary variable within a class of the secondary variable.
- nseccut: number of thresholds to define the classes of secondary variable.
- nlag: the number of variogram lags to consider in the objective function. The closest nlag lags, measured in terms of variogram distance, are retained.
- istand: a flag specifying whether or not to standardize the sill of the semivariogram to the variance of the univariate distribution (istand=1 will standardize). It is essential that the variance of the values of the initial random image matches the spatial (dispersion) variance implied by the variogram model. That dispersion variance should be equal to the total sill if it exists (i.e., a power model has not been used) and the size of the field is much larger than the largest range in the variogram model.
- nst and c0: the number of variogram structures and the isotropic nugget constant
- For each of the nst nested structures one must define it, the type of structure; cc, the c parameter; ang1,ang2,ang3, the angles defining the geometric anisotropy; aa_hmax, the maximum horizontal range; aa_hmin, the minimum horizontal range; and aa_vert, the vertical range. A detailed description of these parameters is given in section II.3.
- Indicator variograms follow the definition of the direct primary variable variogram.