Purpose
Presolves a row formulated in terms of the original variables such that it can be added to a presolved matrix.
Topic areas
Misc, Presolve
Synopsis
colind, rowcoef, rhs, status = problem.presolveRow(rowtype, origcolind, origrowcoef, origrhs)
Arguments
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rowtype
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The type of the row:
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L
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indicates a ≤ row;
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G
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indicates a ≥ row.
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E
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indicates a ≥ row.
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|
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origcolind
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Integer array containing the column indices of the row to presolve.
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origrowcoef
|
Double array containing the non-zero coefficients of the row to presolve.
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origrhs
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The right-hand side constant of the row to presolve.
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Related controls
Integer
|
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Turns presolve on or off.
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|
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Selects the presolve operations.
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Return value
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colind
|
Integer array containing the column indices of the presolved row. Allocate this to
COLS elements and pass
COLS as
maxcoef> to make sure it is large enough to hold the presolved row.
|
|
rowcoef
|
Double array containing the coefficients of the presolved row. Allocate this to
COLS elements and pass
COLS as
maxcoef> to make sure it is large enough to hold the presolved row.
|
|
rhs
|
The presolved right-hand side.
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|
status
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Status of the presolved row:
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-5
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Failed to presolve the row due to presolve operations making the row nonlinear;
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-4
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Failed to presolve the equality row due to presolve operations requiring relaxation of the row;
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-3
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Failed to presolve the row due to presolve dual reductions;
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-2
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Failed to presolve the row due to presolve duplicate column reductions;
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-1
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Failed to presolve the row due to an error. Check the Optimizer error code for the cause;
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0
|
The row was successfully presolved;
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1
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The row was presolved, but may be relaxed.
|
|
Further information
1. There are certain presolve operations that can prevent a row from being presolved exactly. If the row contains a coefficient for a column that was eliminated due to duplicate column reductions or singleton column reductions, the row might have to be relaxed to remain valid for the presolved problem. The relaxation will be done automatically by the
problem.presolveRow function, but a return status of
+1 will be returned. If it is not possible to relax the row, a status of
-2 will be returned instead. Likewise, it is possible that certain dual reductions prevents the row from being presolved. In such a case a status of
-3 will be returned instead. Also transforming a convex quadratic objective transfer row to a convex quadratic objective and nonlinear eliminations will lead to a row not being presolved and return a status of
-5 instead.
2. If
problem.presolveRow will be used for presolving hard constraints, such as e.g. branching bounds or delayed constraints, then dual reductions should be disabled, by setting
MIPDUALREDUCTIONS to 0.
3. If the user knows in advance which columns will have non-zero coefficients in rows that will be presolved, it is possible to protect these individual columns through the
problem.loadSecureVecs function. This way the Optimizer is left free to apply all possible reductions to the remaining columns.
4. Argument
origcolind may contain
xpress.var objects instead of indices.
Related topics
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