Hi,
There is a problem in the functions lpx_write_cpxlp and lpx_read_cpx_lp.
The two operations are not inverses of each other. For instance, when
compiling and executing the file cpxlp_bug.c, a linear programming
problem is created, is written to disk as "a.cpxlp", then read and
written again as "b.cpxlp", and the two files are different.
Also, the program tries to solve the problems with lpx_simplex: the
original has a solution, not the modified one.
Perhaps the bound x_1 <= 0 in "a.cpxlp" should have been written -inf <=
x_1 <= 0 instead.
I am using GLPK version 4.8.
Regards,
Bernard Helmstetter.
#include <stdio.h>
#include <stdlib.h>
#include "glpk.h"
int main()
{
LPX *lp;
int col[1+1];
double val[1+1];
lp = lpx_create_prob();
lpx_set_obj_dir(lp, LPX_MIN);
lpx_add_rows(lp, 1);
lpx_add_cols(lp, 1);
lpx_set_row_bnds(lp, 1, LPX_FX, -1, -1);
lpx_set_col_bnds(lp, 1, LPX_UP, 0, 0);
lpx_set_obj_coef(lp, 1, 1);
col[1] = 1;
val[1] = 1;
lpx_set_mat_row(lp, 1, 1, col, val);
lpx_simplex(lp);
lpx_write_cpxlp(lp, "a.cpxlp");
lpx_delete_prob(lp);
lp = lpx_read_cpxlp("a.cpxlp");
lpx_simplex(lp);
lpx_write_cpxlp(lp, "b.cpxlp");
lpx_delete_prob(lp);
return 0;
}
\* Problem: Unknown *\
Minimize
obj: + x_1
Subject To
r_1: + x_1 = -1
Bounds
x_1 = 0
End
\* Problem: Unknown *\
Minimize
obj: + x_1
Subject To
r_1: + x_1 = -1
Bounds
x_1 <= 0
End
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