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 -1Variables 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
attribute value for each variable in the
model. Note that you can still modify the
attribute after importing an ordering file.