Postsolve Integer Variables

Type : Selection

Range : The settings listed below

Default : Round integers and resolve LP

MIP solvers do not round the found values for the integer variables to the nearest integer value. Instead it returns values which are considered to be integer within the integrality tolerance. This option offers the possibility to perform some postsolving on the found integer solution concerning rounding of integer values. Possible values are:

  • No rounding

  • Round to integer

  • Round integers and resolve LP

If the value equals ‘No rounding’ then the variable values found by the solver are passed directly to AIMMS.

If the value equals ‘Round to integer’ then the integer variable values found by the solver are rounded before passing them to AIMMS.

If the value equals ‘Round integers and resolve LP’ then AIMMS checks whether the solution returned by the solver contains some integer variables that are not really integer. In that case all integer variables are fixed on the nearest integer value, and the LP problem derived in this way is solved. As a result we obtain a solution in which all integer variables have a true integer value.

Note

  • The solving time might increase drastically if the value of this option is set to ‘Round integers and resolve LP’.

  • In case the value of this option is set to ‘No rounding’ or ‘Round to integer’, still the postsolve step can be executed if the value of the option MIP Calculate Sensitivity Information is active. To get sensitivity information, all integer variables have to be fixed and the derived LP problem must be solved.

  • Please check the option Postsolve for more information regarding the postsolve step.

  • For CBC, the option Postsolve should be switched on to activate this option.

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