Robert Fourer
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Latest activity by Robert Fourer-
Robert Fourer commented,
Set Gurobi's nonconvex option in your .run file. If you are already setting a gurobi_options string, then add nonconvex=2 to it. If you are not yet setting a gurobi_options string, then add this c...
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Robert Fourer commented,
The paper by Markowitz was published as Harry M. Markowitz, The Elimination Form of the Inverse and Its Application to Linear Programming. Management Science 3 (1957) 255-269. The situation in wh...
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Robert Fourer commented,
The problem with outlev=1 not showing any log output was caused by a glitch in the build of Gurobi 10.0.1 for AMPL. It is fixed in the most recent build (dated 20230330). The problem with a MIP sta...
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Robert Fourer commented,
When Gurobi 10.0 for AMPL is released (very soon now) there will be an option writepresolvedprob that works the same as the current option writeprob except that it writes -- to the specified file -...
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Robert Fourer commented,
Use AMPL's \(\texttt{.priority}\) suffix to set priorities of variables for Gurobi. For example: suffix priority IN;let {i in ACTIVITIES} Y[i].priority := 100;let {i in ACTIVITIES, t in 1..T} X[i,t...
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Robert Fourer commented,
It appears you are setting an AMPL gurobi_options string. Is newgap an AMPL parameter? Then you need to use an AMPL string expression in an option statement like this: option gurobi_options ("timel...
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Robert Fourer commented,
It's odd that the coefficient statistics show Objective range [0e+00, 0e+00] This suggests that all of the objective coefficients are zero, which would explain why an optimal objective value of 0....
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Robert Fourer commented,
Gurobi's presolve was being turned off when called from AMPL, but was on when called from the R API. This can be seen from the option presolve=0 echoed in the AMPL listing, and the presence of thes...
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Robert Fourer commented,
As mentioned previously, the best bound is returned in the suffix ".bestbound" on the objective. For example, if your objective function is "minimize TotalCost" then the best bound is given by "Tot...
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Robert Fourer commented,
I answered this question in another thread where you asked it today.