# Robert Fourer

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## Activity overview

Latest activity by Robert Fourer
• 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....

• 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...

• 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...

• Robert Fourer commented,

• Robert Fourer commented,

The message "suffix bestbound OUT" says that the suffix .bestbound was created by Gurobi for output to AMPL. It's only an informational message; it appears the first time that Gurobi runs with best...

• Robert Fourer commented,

In AMPL, add bestbound=1 to your gurobi_options string -- or if you are not setting a gurobi_options string yet, give this command before solving: option gurobi_options 'bestbound=1'; Then the best...

• Robert Fourer commented,

For $$a+b+c=0 \Rightarrow d=1$$ with all variables binary, you could write equivalently $$a+b+c+d \geq 1$$, or as an indicator constraint, $$d = 0 \Rightarrow a+b+c \geq 1$$.

• Robert Fourer commented,

This was cross-posted to the AMPL forum, where the issues were resolved.