ORD format

ORD format

A priority ordering (ORD) file is used to input a set of variable priority orders. Reading a priority file (using GRBread, for example) modifies the MIP branch variable selection. When choosing a branching variable from among a set of fractional variables, the Gurobi MIP solver will always choose a variable with higher priority over one with a lower priority.

The file consists of variable-value pairs, each on its own line. The file contains one line for each variable in the model. Any line that starts with the hash sign (#) is treated as a comment line and is ignored. The following is a simple example:

# Branch priority file
x 1
y 1
z -1
Variables have a default branch priority value of 0, so it is not necessary to specify values for all variables.

Importing a priority order file is equivalent to replacing the BranchPriority attribute value for each variable in the model. Note that you can still modify the BranchPriority attribute after importing an ordering file.