# Issue with Excel Solver for optimizing smoothning constant in winthers forecasting model

1. ## Issue with Excel Solver for optimizing smoothning constant in winthers forecasting model

I have the assignment of creating a winthers model for forecasting.

I have to optimize the smoothening constants using the solver, but when i sol using the non-linear function nothing happens.

If there is anyone able to help me locate the issue i would be very grateful.

The task can be found in the tab "Winthers" and the solver parameters should be set up correctly, but is imply cannot figure out why it does not work

BR

OKB1996

2. ## Re: Issue with Excel Solver for optimizing smoothning constant in winthers forecasting mod

tl:dr version -- as written, your objective function (W23) is a step function (a type of nonsmooth function). Small changes in alpha, beta, or gamma results in no change in W23, so Solver thinks it has found the solution.

From Frontline's Solver tutorial, a page about the difficulties of solving nonsmooth problems: https://www.solver.com/nonsmooth-optimization

I don't understand exactly what you are doing here, so I cannot offer anything concrete. A couple of considerations:
As mentioned in the link, perhaps switch to an evolutionary algorithm.
I notice that there are a couple of rounding functions in the computation trail (columns Q, R, and S). Rounding functions are an easy to recognize source of step functions. Are these ROUNDUP() functions absolutely necessary, or could you solve the model without them (then round after finding the solution)?

Basically, you need to figure out how to deal with the step function. Since I don't understand everything that is going on here, I cannot make any concrete suggestions, but perhaps those ideas will allow you to explain what is going on and/or try something.

3. ## Re: Issue with Excel Solver for optimizing smoothning constant in winthers forecasting mod

Hi Shorty

The rounds were messing things up.

Many thanks, I donīt know if it is fully correct, but now my solver is at least doing something

I will compare with my peers to hopefully get the right result. This was my first post in this forum, and i am very glad you would help me!

BR

OKB

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