XPRSaddcbpreintsol
Purpose
Declares a user integer solution callback function, called when an integer solution is found by heuristics or during the branch and bound search, but before it is accepted by the Optimizer. This callback function will be called in addition to any integer solution callbacks already added by XPRSaddcbpreintsol.
Synopsis
int XPRS_CC XPRSaddcbpreintsol(XPRSprob prob, void (XPRS_CC *preintsol)(XPRSprob cbprob, void *cbdata, int soltype, int *p_reject, double *p_cutoff), void *data, int priority);
Arguments
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prob
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The current problem.
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preintsol
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The callback function which takes five arguments,
cbprob,
cbdata,
soltype,
p_reject and
p_cutoff, and has no return value. This function is called when an integer solution is found, but before the solution is accepted by the Optimizer, allowing the user to reject the solution.
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cbprob
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The problem passed to the callback function,
preintsol.
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cbdata
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The user-defined data passed as data when setting up the callback with
XPRSaddcbpreintsol.
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soltype
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The type of MIP solution that has been found: Set to 1 if the solution was found using a heuristic. Otherwise, it will be the optimal (and integer feasible) solution to the current node of the tree search.
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p_reject
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Set this to 1 if the solution should be rejected.
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p_cutoff
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The new cutoff value that the Optimizer will use if the solution is accepted. If the user changes
p_cutoff, the new value will be used instead. The cutoff value will not be updated if the solution is rejected.
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data
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A user-defined data to be passed to the callback function,
preintsol.
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priority
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An integer that determines the order in which callbacks of this type will be invoked. The callback added with a higher priority will be called before a callback with a lower priority. Set to 0 if not required.
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Related controls
Integer
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Branch and Bound: If the user knows that they are interested only in values of the objective function which are better than some value, this can be assigned to MIPABSCUTOFF. This allows the Optimizer to ignore solving any nodes which may yield worse objective values, saving solution time. When a MIP solution is found a new cut off value is calculated and the value can be obtained from the
CURRMIPCUTOFF attribute. The value of
CURRMIPCUTOFF is calculated using the MIPRELCUTOFF and MIPADDCUTOFF controls.
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Example
See also example
tsp.c.
Further information
1. If a solution is rejected, the Optimizer will drop the found solution without updating any attributes, including the cutoff value. To change the cutoff value when rejecting a solution, the control
MIPABSCUTOFF should be set instead.
2. When a node solution (
soltype = 0) is rejected, the node itself will be dropped without further branching.
3. To retrieve the integer solution, use
XPRSgetlpsol,
XPRSgetpresolvesol or
XPRSgetnlpsol.
XPRSgetmipsol will not return the newly found solution because it has not been saved at this point.
4. The current node problem can not be modified in this callback - attempting to add cuts, changing bounds and adding branching objects will raise an error. Any such changes should be applied during the
optnode callback (ref.
XPRSaddcboptnode) when
MIPINFEAS is zero.
5. For this callback attribute
MIPINFEAS is set to -1 if the solution was found by a heuristic.
Related topics
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