Gurobi Always Printing to Console

[cohnt]

What happened?

I've recently observed that when Gurobi is used to solve a MathematicalProgram, the verbose output is always printed to the console. @wernerpe also observed this behavior. For methods that require solving many optimization problems, the output completely clogs the console, and can even crash a jupyter notebook.

Version

16e7281

What operating system are you using?

Ubuntu 22.04, Other

What installation option are you using?

compiled from source code using CMake, compiled from source code using Bazel

Relevant log output

No response

[jwnimmer-tri]

One recent change was #21345, and perhaps I made a mistake there? If you have time, you could try reverting that a let me know if it's to blame.

[cohnt]

No console spam on 44bf559, yes console spam on 40adf9c. So it sounds like that PR added the printing.

[jwnimmer-tri]

Ah. The old code set LogToConsole to 0 or 1 always. The new code only ever sets it to 1. Maybe the Gurobi default is 1?

Does this solve it?

--- a/solvers/gurobi_solver.cc
+++ b/solvers/gurobi_solver.cc
@@ -954,9 +954,7 @@ void GurobiSolver::DoSolve2(const MathematicalProgram& prog,
 
   // Copy the remaining options into model_env.
   options->Respell([](const auto& common, auto* respelled) {
-    if (common.print_to_console) {
-      respelled->emplace("LogToConsole", 1);
-    }
+    respelled->emplace("LogToConsole", common.print_to_console ? 1 : 0);
     if (!common.print_file_name.empty()) {
       respelled->emplace("LogFile", common.print_file_name);
     }

[jwnimmer-tri]

Maybe the Gurobi default is 1?

Yup.

https://www.gurobi.com/documentation/10.0/refman/logtoconsole.html#parameter:LogToConsole

I'll open a PR with that patch and ask for testing.

[cohnt]

Now that I'm manually setting some additional Gurobi parameters (like number of threads), I'm getting spammed again -- this time with messages like Set parameter Threads to value 1 and Set parameter DualReductions to value 0. Is it possible there's some order-dependent thing, where the console printing has to be disabled before other options?

[jwnimmer-tri]

Sigh. I imagine the full solution is to call a hard-coded SetOptionOrThrow("LogToConsole", 0); as early as possible during DoSolve2, before doing anything else.

[jwnimmer-tri]

BTW I don't have a lot of time today, and I don't have convenient access to a Gurobi license to test, so I'd welcome any contributors' fixes.

[cohnt]

I can confirm that dropping that in anytime before options->CopyToCallbacks is called in gurobi_solver.cc removes the extra print statements, but then those statements don't always come back if kPrintToConsole is set to true. (That doesn't bother me, but I can understand why it might bother someone.)