Solver not resulting in min
Solver not resulting in min
(OP)
I am trying to use excel's solver to minimize a very complex function that is subject to six constraints(optimizing the number of fins on a heat sink), but the solver never hits the minimum value, when I plot the function versus the number of fins, there is always a lower value(greater number of fins) than the solver outputs...and yes there is a min to my function, looks like a parabola
has anyone every come across this and hopefully have a solution
has anyone every come across this and hopefully have a solution





RE: Solver not resulting in min
Also you mentioned many constraints, is it possible that the minimum that you saw on your graph is outside of your constraints?
I have seen solver do some strange things that I can't explain. Sometimes it seems like it makes a difference in what order you define the variables to be changed.
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Solver not resulting in min
how does the solver come up with a solution? does it test values outside the constraints and then filters the results to the constraints or is just ignoring my constraints?
RE: Solver not resulting in min
I suspect that it will only try solutions that meet input constraints, and will take less or no notice of results that exceed mixed or output constraints (depending on how much).
There is quite a bit of literature around on how the solver works, it is a crippled version of a commercial product.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Solver not resulting in min
RE: Solver not resulting in min
RE: Solver not resulting in min
RE: Solver not resulting in min
TTFN
Eng-Tips Policies FAQ731-376
RE: Solver not resulting in min
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Solver not resulting in min
No algorithm exists will find the global minimum in a space of local minima (please refute and provide example if you have one! I'd be extremely interested in the algorithm that is guaranteed to find the global minimum). For instance, imagine if you had a surface in just a 3D space; the surface has lots of dips and peaks, so that there are lots of local minima but only one, global minimum. If you know the function that maps the surface, make an initial guess near a local minima which IS NOT the global minima, than your solver might find that local minima after a few iterations. Or it might not. Either way, just be looking at computer output, you won't know whether your minimum is a local one or the global one.
RE: Solver not resulting in min
RE: Solver not resulting in min
Of course if you can improve your initial guess then the Solver is a fast solution to find the local optimum.
Typically I'd use GA or just a random exploration, depending on the size of the problem.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.