8 Debugging Tutorials

This collection of tutorials contains basic techniques for debugging optimization problems using tools available in MOSEK: optimizer log, solution summary, infeasibility report, command-line tools. It is intended as a first line of technical help for issues such as: Why do I get solution status unknown and how can I fix it? Why is my model infeasible while it shouldn’t be? Should I change some parameters? Can the model solve faster? etc.

The major steps when debugging a model are always:

  • Consult the log output. It is enabled by default, but if neccessary switch it on explicitly with:

model.solve(quiet = false);

  • Run the optimization and analyze the log output, see Sec. 8.1 (Understanding optimizer log). In particular:

    • check if the problem setup (number of constraints/variables etc.) matches your expectation.

    • check solution summary and solution status.

  • Dump the problem to disk if necessary to continue analysis. See Sec. 6.3.3 (Saving a problem to a file).

    • use a human-readable text format, preferably *.ptf if you want to check the problem structure by hand. Assign names to variables and constraints to make them easier to identify.

      % Before solving:
model.solve(write_to_file = "dump.ptf");
% or without solving:
model.write("dump.ptf");

    • use the MOSEK native format *.task.gz when submitting a bug report or support question.

      % Before solving:
model.solve(write_to_file = "dump.task.gz");
% or without solving:
model.write("dump.task.gz");

  • Fix problem setup, improve the model, locate infeasibility or adjust parameters, depending on the diagnosis.

See the following sections for details.