If my previous rationale is correct we also need the same change for the
LP processing in "src/draft/glpapi06.c":
=====
@@ -289,11 +289,11 @@ static int preprocess_and_solve_lp(glp_prob *P,
const glp_smcp *parm)
/* build transformed LP */
lp = glp_create_prob();
npp_build_prob(npp, lp);
/* if the transformed LP is empty, it has empty solution, which
is optimal */
- if (lp->m == 0 && lp->n == 0)
+ if (lp->m == 0 || lp->n == 0)
{ lp->pbs_stat = lp->dbs_stat = GLP_FEAS;
lp->obj_val = lp->c0;
if (parm->msg_lev >= GLP_MSG_ON && parm->out_dly == 0)
{ xprintf("~%6d: obj = %17.9e infeas = %10.3e\n", P->it_cnt,
lp->obj_val, 0.0);
=====
On 13/7/20 18:31, Domingo Alvarez Duarte wrote:
Hello !
In my opinion the fix for this problem could be here in
"src/draft/glpapi09.c" (see patch bellow) because doesn't seem to make
sense go forward if the presolved/preprocessed problem has zero rows
or zero columns, another possibility is a bad (generated) problem and
if that is the case the fix should be in detecting the bad problem.
=====
@@ -324,11 +324,11 @@ static int preprocess_and_solve_mip(glp_prob *P,
const glp_iocp *parm)
/* build transformed MIP */
mip = glp_create_prob();
npp_build_prob(npp, mip);
/* if the transformed MIP is empty, it has empty solution, which
is optimal */
- if (mip->m == 0 && mip->n == 0)
+ if (mip->m == 0 || mip->n == 0)
{ mip->mip_stat = GLP_OPT;
mip->mip_obj = mip->c0;
if (parm->msg_lev >= GLP_MSG_ALL)
{ xprintf("Objective value = %17.9e\n", mip->mip_obj);
xprintf("INTEGER OPTIMAL SOLUTION FOUND BY MIP PREPROCESSOR"
=====
Cheers !
On 13/7/20 15:25, Peter Cawley wrote:
Hi all,
The enclosed s.lp is solvable by GLPK 4.61:
-----
$ glpk-4.61/examples/glpsol --glp s.lp
GLPSOL: GLPK LP/MIP Solver, v4.61
Parameter(s) specified in the command line:
--glp s.lp
Reading problem data from 's.lp'...
81 rows, 48 columns, 168 non-zeros
48 integer variables, none of which are binary
331 lines were read
GLPK Integer Optimizer, v4.61
81 rows, 48 columns, 168 non-zeros
48 integer variables, none of which are binary
Preprocessing...
1 row, 0 columns, 0 non-zeros
0 integer variables, none of which are binary
Scaling...
A: min|aij| = 1.000e+00 max|aij| = 1.000e+00 ratio = 1.000e+00
Problem data seem to be well scaled
Solving LP relaxation...
GLPK Simplex Optimizer, v4.61
1 row, 0 columns, 0 non-zeros
~ 0: obj = 0.000000000e+00 infeas = 0.000e+00
OPTIMAL SOLUTION FOUND
Integer optimization begins...
+ 0: mip = not found yet >= -inf (1; 0)
+ 0: >>>>> 0.000000000e+00 >= 0.000000000e+00 0.0% (1; 0)
+ 0: mip = 0.000000000e+00 >= tree is empty 0.0% (0; 1)
INTEGER OPTIMAL SOLUTION FOUND
Time used: 0.0 secs
Memory used: 0.1 Mb (80560 bytes)
-----
But causes an internal failure with GLPK 4.65:
-----
$ glpk-4.65/examples/glpsol --glp s.lp
GLPSOL: GLPK LP/MIP Solver, v4.65
Parameter(s) specified in the command line:
--glp s.lp
Reading problem data from 's.lp'...
81 rows, 48 columns, 168 non-zeros
48 integer variables, none of which are binary
331 lines were read
GLPK Integer Optimizer, v4.65
81 rows, 48 columns, 168 non-zeros
48 integer variables, none of which are binary
Preprocessing...
1 row, 0 columns, 0 non-zeros
0 integer variables, none of which are binary
Scaling...
A: min|aij| = 1.000e+00 max|aij| = 1.000e+00 ratio = 1.000e+00
Problem data seem to be well scaled
Solving LP relaxation...
GLPK Simplex Optimizer, v4.65
1 row, 0 columns, 0 non-zeros
~ 0: obj = 0.000000000e+00 infeas = 0.000e+00
OPTIMAL SOLUTION FOUND
Integer optimization begins...
glp_add_cols: ncs = 0; invalid number of columns
Error detected in file api/prob1.c at line 362
Abort trap: 6
-----
According to LLDB, the call stack at the point of failure is:
-----
* frame #0: 0x00007fff570acb66
libsystem_kernel.dylib`__pthread_kill + 10
frame #1: 0x00007fff57277080 libsystem_pthread.dylib`pthread_kill
+ 333
frame #2: 0x00007fff570081ae libsystem_c.dylib`abort + 127
frame #3: 0x0000000100105a7d
libglpk.40.dylib`errfunc(fmt=<unavailable>) at error.c:55 [opt]
frame #4: 0x00000001000c03c9
libglpk.40.dylib`glp_add_cols(lp=0x0000000100401b10, ncs=0) at
prob1.c:362 [opt]
frame #5: 0x00000001000eab84
libglpk.40.dylib`_glp_ios_create_tree [inlined]
_glp_ios_create_pool(tree=<unavailable>) at glpios01.c:1395 [opt]
frame #6: 0x00000001000eab6a
libglpk.40.dylib`_glp_ios_create_tree(mip=<unavailable>,
parm=0x00007ffeefbff608) at glpios01.c:129 [opt]
frame #7: 0x00000001000e3eda
libglpk.40.dylib`solve_mip(P=0x0000000100400f60,
parm=0x00007ffeefbff608, P0=0x0000000100400310,
npp=0x0000000100400080) at glpapi09.c:244 [opt]
frame #8: 0x00000001000e3d2c libglpk.40.dylib`glp_intopt
[inlined] preprocess_and_solve_mip(P=<unavailable>) at glpapi09.c:415
[opt]
frame #9: 0x00000001000e391a
libglpk.40.dylib`glp_intopt(P=<unavailable>, parm=0x0000000000000000)
at glpapi09.c:634 [opt]
frame #10: 0x00000001000031d4 glpsol`main(argc=<unavailable>,
argv=0x42773482f5d96a00) at glpsol.c:1423 [opt]
-----
Based on a very superficial understanding of the code, guarding the
`glp_add_cols(pool, tree->mip->n);` call within `ios_create_pool`
with `if (tree->mip->n)` seems to sidestep the failure, but perhaps a
more involved fix is required.
Regards,
Peter
