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MST format


MST format

A MIP start (MST) file is used to specify an initial solution for a mixed integer programming model. The file lists values to assign to the variables in the model. If a MIP start has been imported into a MIP model before optimization begins (using GRBread, for example), the Gurobi optimizer will attempt to build a feasible solution from the specified start values. A good initial solution often speeds the solution of the MIP model, since it provides an early bound on the optimal value, and also since the specified solution can be used to seed the local search heuristics employed by the MIP solver.

A MIP start file consists of variable-value pairs, each on its own line. Any line that begins with the hash sign (#) is a comment line and is ignored. The following is a simple example:

# MIP start
x1  1
x2  0
x3  1

Importing a MIP start into a model is equivalent to setting the Start attribute for each listed variable to the associated value. If the same variable appears more than once in a start file, the last assignment is used. Importing multiple start files is equivalent to reading the concatenation of the imported files.

Note that start files don't need to specify values for all variables. When variable values are left unspecified, the Gurobi solver will try to extend the specified values into a feasible solution for the full model.

It is important to mention that when saving an MST file, Gurobi will not save the values of continuous variables. If you want to save a complete description of the best solution found, we recommend to save it as a solution file (SOL format). This will guarantee that you will save the values for each variable present in your model.