Re: Regression between 4.61 and 4.65 for problems which can be preprocessed to almost nothing

[Andrew Makhorin]

Thank you for your bug report.


Running glpsol 4.65 with the command:

glpsol --glp s.lp

indicates the following error:

[...]
OPTIMAL SOLUTION FOUND
Integer optimization begins...
glp_add_cols: ncs = 0; invalid number of columns
Error detected in file src/api/prob1.c at line 362

SIGABRT signal raised, execution terminated

Call traceback
func __abend, file ../c.lib/src/xabend.c, line 45
func raise, file ../c.lib/src/raise.c, line 76
func abort, file ../c.lib/src/abort.c, line 51
func errfunc, file src/env/error.c, line 55
func glp_add_cols, file src/api/prob1.c, line 362
func _glp_ios_create_pool, file src/draft/glpios01.c, line 1395
func _glp_ios_create_tree, file src/draft/glpios01.c, line 129
func solve_mip, file src/draft/glpapi09.c, line 244
func preprocess_and_solve_mip, file src/draft/glpapi09.c, line 415
func glp_intopt, file src/draft/glpapi09.c, line 634
func main, file examples/glpsol.c, line 1423
func __c0, file ../c.lib/src/woe/c0.c, line 58
End of traceback

Program abnormally terminated


>From the call traceback it is seen that the internal routine
ios_create_pool attempts to add 0 columns that causes the error.

To fix the bug please modify the routine ios_create_pool (file
src/draft/glpios01.c, lines 1391-1397) as follows:

IOSPOOL *ios_create_pool(glp_tree *tree)
{     /* create cut pool */
      IOSPOOL *pool;
      pool = glp_create_prob();
#if 1 /* 14/VII-2020 */
      if (tree->mip->n)
#endif
      glp_add_cols(pool, tree->mip->n);
      return pool;
}


Once the bug has been fixed, glpsol runs successfully:

[...]
OPTIMAL SOLUTION FOUND
Integer optimization begins...
Long-step dual simplex will be used
+     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 (60952 bytes)







On Mon, 2020-07-13 at 14:25 +0100, 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
>