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From: | Peter Cawley |
Subject: | Re: Regression between 4.61 and 4.65 for problems which can be preprocessed to almost nothing |
Date: | Mon, 13 Jul 2020 16:14:53 +0100 |
Hello Peter !
Do you have the original model/data that was used to generate the "s.lp" ?
Maybe the problem is in the bad model generation instead.
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
>
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