The REPROD parameter allows you to indicate if your preference is for reproducible solutions across multiple runs.  In general, being able to reproduce results is a desirable outcome. However, some models may run faster if we opt to not favor reproducible runs.

A number of solver steps have been found to perform better when using elapsed time as a measure of work performed.  The problem with this approach is that the actual amount of work that gets performed over a fixed time interval will vary slightly across runs depending on a machine's load factor.  Many models have alternate optimal solutions, with equal objectives but different variable values.  LINGO is indifferent as to which solution is selected; it just wants to find a feasible solution with the best objective value, regardless of the variables values.  The end result of this variability in work performed is that a different solution path may be selected from one run to the next, in which case, you may end up with a different alternate optimum from a previous run.

On the other hand, enabling the REPROD option causes LINGO to use fixed measures of work (such as iteration counts), allowing solutions to be reproducible across runs when using the same machine.

By default, LINGO enables the REPROD option.