## GSLIB Help Page: LUSIM

Description:

- Creates Gaussian-based realizations with LU matrix method

Parameters:

- datafl: the input data are in a simplified Geo-EAS formatted file.
- 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.
- idbg: an integer debugging level between 0 and 3. The higher the debugging level the more output.
- dbgfl: a file for the debugging output.
- outfl: the output grid is written to this file. The output file will contain the grid, cycling fastest on x then y then z and last per simulation.
- nsim: the number of simulations 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).
- 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.

Application notes:

- This program requires standard normal data and writes standard normal simulated values. Normal score transform and back transform are to be performed outside of this program
- Recall that the power model is not a legitimate model for a multiGaussian phenomenon and it is not allowed in `lusim`
- The semivariogram model is that of the normal scores. The kriging variance is directly interpreted as the variance of the conditional distribution; consequently, the nugget constant c0 and c (sill) parameters should add to 1.0.