Hi,

The reason I do a manual run of Solver before I run the VBA is so that I do not need to reset the Solver for every iteration. So, say I have 1000 iterations, I just need to reuse the same constraints over and over again. If I were to do a SolverReset before each run, it would take even more time. Of course, I re-initialise my parameters to some fixed values before I run each Solver, so I think there is no constrain-build up that you mention. And I cannot use Simplex because my problem is nonlinear.

Currently I do not have a sample file to upload -- the files that I am working with were not created by me, and they are huge (>10MB per file). Basically, there is this super long equation (with power laws, exponentials, trigonometry, and integration steps somewhere in between, etc) that needs a lot of prior steps to arrive at, and there are a handful of parameters that need to be optimized so that the difference between this model and some measured values are as similar as possible. As you can imagine, each run of the Solver involves easily tens of thousands of calculations. I am just hoping to cut down the run time by directly calling the dll rather then invoking the GUI-based Solver.