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[Bug-glpk] Re: Glpk bug?


From: Andrew Makhorin
Subject: [Bug-glpk] Re: Glpk bug?
Date: Thu, 5 Jul 2007 22:46:10 +0400

> I have a problem to solve the given MIP with Glpk. It aborts with the
> following error message:

>> glpsol --intopt --cpxlp optconfig-solve.lp-glpk.lp

> GLPK internal error: x >= lb; file glpmip02.c, line 228

> I am using version 4.18, but the error is the same for 4.4 and 4.15.

> ILOG Cplex solves the given MIP successfully, so I guess it is OK.

> Is there any fix for this bug?

This is not a bug, but a defect of the b&b solver.

The error happens due to excessive round-off errors, which, in turn,
happen due to huge bounds of some integer variables. For example:

0 <= gmodeli_p2_p5 <= 2147483647

It would be better not to specify the upper bound at all.

Nevertheless, adding the option '--cgr' I managed to solve your
instance to optimality:

lpx_read_cpxlp: reading problem data from `bug.lp'...
lpx_read_cpxlp: 3226 rows, 1932 columns, 8937 non-zeros
lpx_read_cpxlp: 1932 integer columns, 1878 of which are binary
lpx_read_cpxlp: 7626 lines were read
ipp_basic_tech:  418 row(s) and 60 column(s) removed
ipp_reduce_bnds: 2 pass(es) made, 488 bound(s) reduced
ipp_basic_tech:  452 row(s) and 450 column(s) removed
ipp_reduce_coef: 2 pass(es) made, 20 coefficient(s) reduced
lpx_intopt: presolved MIP has 2356 rows, 1422 columns, 5973 non-zeros
lpx_intopt: 1422 integer columns, 1377 of which are binary
lpx_adv_basis: size of triangular part = 2356
Solving LP relaxation...
      0:   objval =   1.754620000e+05   infeas =   1.000000000e+00 (0)
    200:   objval =   5.682940000e+05   infeas =   4.678937555e-04 (0)
    400:   objval =   5.683725057e+05   infeas =   4.676103586e-04 (0)
    600:   objval =   6.758156656e+05   infeas =   2.033088516e-05 (0)
    619:   objval =   6.768716656e+05   infeas =   2.525222006e-20 (0)
*   619:   objval =   6.768716656e+05   infeas =   1.987299214e-14 (0)
*   800:   objval =   6.645538361e+05   infeas =   2.999919154e-14 (0)
*  1000:   objval =   5.714568399e+05   infeas =   1.393510204e-15 (0)
*  1054:   objval =   5.684413548e+05   infeas =   1.009830884e-13 (0)
OPTIMAL SOLUTION FOUND
Integer optimization begins...
Objective function is integral
+  1054: mip =     not found yet >=              -inf        (1; 0)
+  1590: mip =     not found yet >=   5.684420000e+05        (9; 0)
+  1656: mip =     not found yet >=   5.684420000e+05        (18; 0)
+  1666: mip =     not found yet >=   5.684420000e+05        (28; 0)
+  1677: mip =     not found yet >=   5.684420000e+05        (39; 0)
+  1687: mip =     not found yet >=   5.684420000e+05        (49; 0)
+  1698: mip =     not found yet >=   5.684420000e+05        (60; 0)
+  1710: mip =     not found yet >=   5.684420000e+05        (72; 0)
+  1721: mip =     not found yet >=   5.684420000e+05        (83; 0)
+  1732: mip =     not found yet >=   5.684420000e+05        (94; 0)
+  2217: mip =     not found yet >=   5.684420000e+05        (108; 0)
+  2277: mip =   5.696190000e+05 >=   5.684420000e+05   0.2% (167; 0)
+  3231: mip =   5.696190000e+05 >=   5.684420000e+05   0.2% (90; 146)
+  4364: mip =   5.696190000e+05 >=   5.684420000e+05   0.2% (54; 193)
+  4742: mip =   5.696190000e+05 >=   5.684420000e+05   0.2% (83; 193)
+  5529: mip =   5.696190000e+05 >=   5.684420000e+05   0.2% (99; 195)
+  6404: mip =   5.696190000e+05 >=   5.684420000e+05   0.2% (124; 197)
+  7562: mip =   5.696190000e+05 >=   5.684420000e+05   0.2% (138; 207)
+  7980: mip =   5.696190000e+05 >=   5.684420000e+05   0.2% (131; 242)
+  8227: mip =   5.696190000e+05 >=   5.684420000e+05   0.2% (155; 247)
+  8475: mip =   5.696190000e+05 >=   5.684420000e+05   0.2% (174; 255)
+  8526: mip =   5.685620000e+05 >=   5.684420000e+05 < 0.1% (224; 255)
+  9348: mip =   5.685620000e+05 >=   5.685330000e+05 < 0.1% (65; 591)
+  9611: mip =   5.685620000e+05 >=     tree is empty   0.0% (0; 855)
INTEGER OPTIMAL SOLUTION FOUND
Time used:   113.0 secs
Memory used: 5.1 Mb (5371216 bytes)






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