[Symphony] warm_solve getting stuck?

[Ross Anderson]

Hi all,

I'm attempting a warm start on a large MIP. I'm having trouble
creating a minimal example, so for now I'll keep this general and hope
there's an easy fix.
The original solution works fine. I call sym_solve(env); with options
keep_warm_start=TRUE
node_limit=8000
do_reduced_cost_fixing=0

and I get a solution.
Then I reset some params

sym_set_int_param(env, "do_reduced_cost_fixing", 0); //this one is
repeated so that I don't receive SYMPHONY can not resolve for the obj
coeff change when reduced cost fixing is on
sym_set_int_param(env, "node_limit", -1);

I reset some obj coeffs,
sym_set_obj_coeff(env, 142, -1);

and resolve
sym_warm_solve(env);

Screen output starts repeatedly saying
done: 10639 left: 2 ub: -886.16 lb: -886.15 gap: 0.00 time: 820
....The time increments each line, but "done", "left", "ub", "lb", and
"gap" don't change. This happens until I kill the process.

If I instead begin the problem with the 142'th variable objective
coefficient set to -1 (ie. without the warm start), everything works
fine.


Why is this getting stuck?

Thank you