Bug fix: solution incorrect when simplex presolve removes empty columns#29
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rapids-bot[bot] merged 4 commits intoNVIDIA:branch-25.05from May 23, 2025
chris-maes:fix_presolve_removed_empty_cols
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Bug fix: solution incorrect when simplex presolve removes empty columns#29rapids-bot[bot] merged 4 commits intoNVIDIA:branch-25.05from chris-maes:fix_presolve_removed_empty_cols
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chris-maes:fix_presolve_removed_empty_cols
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…ns (NVIDIA#29) Fixes an issue reported on the following MPS file, where `_dummy` variable does not appear in the constraints. We remove empty columns (and thus `_dummy`) in presolve for dual simplex. But do not take this into account when constructing the solution. Further work, is needed to develop an actual LP presolve. ``` *SENSE:Minimize NAME test_export_dict_LP_no_obj ROWS N OBJ G c1 E c2 L c3 G c4 COLUMNS __dummy OBJ 1.000000000000e+00 w c4 1.000000000000e+00 x c1 1.000000000000e+00 x c2 1.000000000000e+00 y c1 1.000000000000e+00 y c3 -1.000000000000e+00 z c2 1.000000000000e+00 z c3 1.000000000000e+00 RHS RHS c1 5.000000000000e+00 RHS c2 1.000000000000e+01 RHS c3 7.000000000000e+00 RHS c4 0.000000000000e+00 BOUNDS FX BND __dummy 0.000000000000e+00 FX BND w 0.000000000000e+00 UP BND x 4.000000000000e+00 LO BND y -1.000000000000e+00 UP BND y 1.000000000000e+00 ``` Fixes NVIDIA#13 which was caused by an issue in column scaling when the norm of a column is zero. Authors: - Chris Maes (https://github.com/chris-maes) Approvers: - Rajesh Gandham (https://github.com/rg20) - Nicolas Blin (https://github.com/Kh4ster) URL: NVIDIA#29
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Fixes an issue reported on the following MPS file, where
_dummyvariable does not appear in the constraints. We remove empty columns (and thus_dummy) in presolve for dual simplex. But do not take this into account when constructing the solution.Further work, is needed to develop an actual LP presolve.
Fixes #13 which was caused by an issue in column scaling when the norm of a column is zero.