Fourier-Motzkin presolve - #3191

Merged

Opt-Mucca merged 237 commits into

Aug 21, 2026

Commits on Apr 28, 2026

Commits on Apr 29, 2026

More WIP
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Return Result::kOk
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WIP
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Commits on Apr 30, 2026

Re-set pointers for bound vectors
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Skip deleted rows
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Commits on May 5, 2026

WIP
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Commits on May 6, 2026

Commits on May 7, 2026

Restarts still not working
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Commits on May 8, 2026

Merge branch 'latest' of https://github.com/ERGO-Code/HiGHS into presolveAddRowsDebugging3
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WIP
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Still WIP
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WIP
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Pass reference to postsolve stack to undo
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Still WIP
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Undo change
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Commits on May 11, 2026

WIP
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Merge branch 'latest' of https://github.com/ERGO-Code/HiGHS into presolveAddRowsDebugging5
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Commits on May 12, 2026

Argh, still WIP
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WIP
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Commits on May 13, 2026

WIP
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WIP
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Merge branch 'latest' of https://github.com/ERGO-Code/HiGHS into presolveAddRowsDebugging6
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And WIP again
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Fix issue in unsed code
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Add indicator for row type
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WIP
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WIP
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Add utility methods
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Commits on May 18, 2026

Rename
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WIP
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Format
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WIP
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WIP
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Merge branch 'latest' of https://github.com/ERGO-Code/HiGHS into presolveAddRowsDebugging7
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WIP
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Merge branch 'presolveAddRowsDebugging7' of https://github.com/fwesselm/HiGHS into presolveAddRowsDebugging7
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WIP
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Remove extra variable
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Remove debugging code
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Commits on May 19, 2026

WIP
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Commits on May 26, 2026

Commits on May 28, 2026

Merge branch 'presolveAddRows7' of https://github.com/fwesselm/HiGHS into fourierMotzkin1
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WIP
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Clean up
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Simplify
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Heap
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Resize singleEquationChecked
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Simplify again
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Add flag
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Merge branch 'fourierMotzkin2' of https://github.com/fwesselm/HiGHS into fourierMotzkin2
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Add message
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Rename
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Merge branch 'fourierMotzkin2' of https://github.com/fwesselm/HiGHS into fourierMotzkin2
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Bound handling
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Commits on May 29, 2026

Initialise
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Add another lambda to check if column is a candidate
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Merge branch 'fourierMotzkin2' of https://github.com/fwesselm/HiGHS into fourierMotzkin2
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Format
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Remove check
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Clean up
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Postolve
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WIP
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WIP
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Commits on Jun 1, 2026

WIP
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WIP
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WIP
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WIP
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Commits on Jun 2, 2026

WIP
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WIP
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Commits on Jun 3, 2026

WIP
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WIP
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WIP
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WIP
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WIP
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Remove debugging code
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Apply only once
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Revert change for debugging
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Commits on Jun 5, 2026

Use implied bounds and remove debug print
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Fix build error
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Skip cols with non-zero objective coefficient
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Add artificial variable for objective
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Commits on Jun 8, 2026

WIP
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Resize
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Fix reformulation
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00fc8f0
Fix pseudo cost
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Fix basis
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WIP
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WIP
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More postsolve changes
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Fix postsolve
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New lambda
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Simplify
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Merge branch 'latest' of https://github.com/ERGO-Code/HiGHS into FMPresolve
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Reformulate only if needed
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Fix output alignment
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Remove extra check
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Commits on Jun 9, 2026

Enable on LPs
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Clean up
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Use static_cast
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bb2faca
Allow multiple rounds of FM presolve
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Minor changes
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Still issues with basis postsolve
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Commits on Jun 10, 2026

Rework postsolve
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Formatted
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Simplify
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Simplify again
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Comments
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Simplify some more
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Fix merge
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Try on LPs again
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Fix test
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Clean up postsolve
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Comments
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Simplify postsolve and use HighsCDouble if needed
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Merge
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Store correct scaling
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Commits on Jun 11, 2026

Primal postsolve
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Clean up some more
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Fix comment
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Clean up
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Comment
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Clean up
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Clean up
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Primal postsolve as in paper
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Dual postsolve fix for ranged rows
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Fix col dual
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Basis postsolve again
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Basis postsolve again
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Primal postsolve and FME column index changes
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Modified reformulation logic
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Clean up
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ec5d2b1
Move lambda
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Commits on Jun 12, 2026

Basis postsolve still not working
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Merge branch 'latest' of https://github.com/ERGO-Code/HiGHS into FMPresolve3
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cb8e864
Minor change
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Resize vector
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Simplify some more
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06cb5ec

Commits on Jun 22, 2026

Merge branch 'latest' of https://github.com/ERGO-Code/HiGHS into FMPresolve3
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Move logic to postsolve
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Comment
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Try to simplify a little more
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Remove unused code
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fc0aec0
Use checkLimits() correctly
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Use tolerance in primal postsolve
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Merge branch 'FMPresolve3' of https://github.com/fwesselm/HiGHS into FMPresolve3
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745e4b4
Clean up
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b2da68c
Merge branch 'latest' of https://github.com/ERGO-Code/HiGHS into FMPresolve3
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Merge branch 'FMPresolve3' of https://github.com/fwesselm/HiGHS into FMPresolve3
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Reset stale values
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bdcc554

Commits on Jun 23, 2026

Fix sc50b
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Use global bounds
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Add postsolve handling for rows that were converted to equations
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Commits on Jun 24, 2026

Cost should be zero
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Working on basis postsolve again
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Basis postsolve
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Fix handling of ranged rows
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Add an assertion
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Comment out assertion about numbers of rows/columns in TestCAPI
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Remove unused code
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Switch off FM for distillation LP
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Fix test
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Mark col as deleted before removing rows
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Commits on Jun 25, 2026

Merge latest
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Fix test after merge
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Commits on Jun 26, 2026

Add lambda for logging
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Use HighsHashTable
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Fix log message
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Switch back to unordered_map
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Redundancy checks
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Added specific FM test to TestPresolveRules.cpp and reworded FM reduciton statement
Julian Hall
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Merge branch 'latest' into FMPresolve4-jh
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Merged latest into this branch
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Constructed simple example giving simplex iteration after postsolve
Julian Hall
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Derived failing FM postsolve test
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329f0ee
Cleaned up; formatted
Julian Hall
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Fix check
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Commits on Jun 29, 2026

Fix basis postsolve
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Remove debug printfs
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Don't run failing test
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Merge branch 'latest' of https://github.com/ERGO-Code/HiGHS into FMPresolve4-jh
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Merge branch 'latest' of https://github.com/ERGO-Code/HiGHS into FMPresolve4-jh
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Merge branch 'FMPresolve4-jh' of https://github.com/fwesselm/HiGHS into FMPresolve4-jh
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Merge branch 'latest' of https://github.com/ERGO-Code/HiGHS into FMPresolve5
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cb347de
Merge branch 'FMPresolve4-jh' of https://github.com/fwesselm/HiGHS into FMPresolve5
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5cb87dc
Clean up
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Enable test but skip PDLP
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32924a4
Simplify
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Commits on Jun 30, 2026

Commits on Jul 2, 2026

Sort candidates
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Add heap struct
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Merge branch 'latest' of https://github.com/ERGO-Code/HiGHS into FMPresolve5
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605a097

Commits on Jul 3, 2026

Move some code around
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Stop early
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Add tryFourierMotzkin flag
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Fix flag
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Simplify
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Commits on Jul 6, 2026

Merge branch 'latest' of https://github.com/ERGO-Code/HiGHS into FMPresolve5
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aefaca0
Tidy up HPresolve::dominatedColumns
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ca7294a

Commits on Jul 15, 2026

Commits on Aug 3, 2026

Merge with latest
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Commits on Aug 5, 2026

Commits on Aug 6, 2026

Merge branch 'latest' of https://github.com/ERGO-Code/HiGHS into FMPresolve5
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3baff29

Commits on Aug 7, 2026

Don't build vector of non-zero objective coefficients if it is not used
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6633cf7
Merge branch 'FMPresolve5' of https://github.com/ERGO-Code/HiGHS into FMPresolve5
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484a8a7
Clear original row index
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3c926e9
Merge branch 'FMPresolve5' of https://github.com/fwesselm/HiGHS into FMPresolve5
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Fix commented out line
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Fix tolerance
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06b577d

Commits on Aug 10, 2026

Merge
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Merge chaser
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Disable FM in presolve light mode
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b98ebc4
Merge branch 'latest' of https://github.com/fwesselm/HiGHS into FMPresolve6
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cca4f83
Minor change; use size_t
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bf3a382
Fix usage of allow_rule_
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2bd1e5c

Commits on Aug 11, 2026