On Tue, Aug 12, 2008 at 12:49 AM, Andrew Makhorin
<address@hidden> wrote:
> Few days back, there was a discussion on the mailing list about
> sparse and dense constraint coefficient matrices. I thought it would
> be nice to be able to visualize matrix A and "see" how much sparse it
> is. This might help verify, understand and debug LP/MIP models created
> using MathProg.
Glpk includes some internal routines for such purpose (see glpspm.c),
in particular, spm_show_mat to write the sparse matrix pattern in bitmap
format. However, I do not know if it is reasonable to carry out such
routines on api level.
I just played around these functions, seems to be working fine. For small matrices the BMP images would be too small. For 10 X 10 matrix, it would 10 X 10 pixel image.
Did you create these functions and structures like SPM to debug in initial stages of GLPK development?
--------------------------------------------------------------------------------
/* Matrix Visualisation. Create 300x300 pixel BMP file.
* Vijay Patil
* */
#include<stdio.h>
#include<stdlib.h>
#include "glpspm.h"
#define ROWCNT 300
#define COLCNT 300
int main(void)
{
SPM * matrix = NULL;
int ri, ci;
matrix = spm_create_mat(ROWCNT, COLCNT);
for(ri = 1; ri <= ROWCNT; ri++) {
for(ci = 1; ci <= COLCNT; ci++) {
if(ri == ci)
spm_new_elem(matrix, ri, ci, 1.0); // WHITE
else if(ri == COLCNT - ci)
spm_new_elem(matrix, ri, ci, -1.0); // CYAN
else if(ri == ROWCNT/2)
spm_new_elem(matrix, ri, ci, 0.0); // GREEN
// Other cells should be BLACK
}
}
spm_show_mat(matrix, "matrix.bmp");
system("gimp -s matrix.bmp &");
spm_delete_mat(matrix);
return 0;
}
--
Vijay Patil
matrix.bmp