Prior

Variables in mixed integer programs can have a priority attribute.  The user can use this parameter to specify an order for picking variables to branch on during a branch and bound search for MIP model solution.  Without priorities, the MIP algorithm will determine the variable most suitable to branch on.  One must also tell GAMS statement to use priorities by entering

modelname.prioropt = 1 ;

where modelname is the name of the model specified in the model statement.  The default value is 0 in which case priorities will not be used.  Using the .prior attribute sets the priorities of the individual variables.  Priorities can be set to any real value.  The default value is 1.0.  As a general rule of thumb, the most important variables should be given the highest priority which implies they should have the lowest nonzero values of the .prior attribute.  The attribute is addressed using .Prior as follows

Variable priority is variablename.prior(setdependency)

These are commonly used in calculations pre solution to specify or revise the priority factors.

Example:

Move.prior("boston","seattle")=1.;

Notes: