VBA EXCEL Fitting Curve with freely chosen functio

Question

As start situation, I have an xy-chart with some values on it whose progression resemble an exponential function. I need to write a code that draws a fitting curve on the chart, but I have to use a particular function which is not exponential (because I need to get some coefficients from it).

One of the functions i need to use is K(C-x)²/(1+x) whereby k and C are the parameters I need.(They are two and it makes it a lot more complicated) Obviously you can't find this kind of structure on the fitting curve tool in Excel. Is there any possibility to have a fitting curve to a chart where you can write yourself the structure of the function?

Sorry if I don't add any written code, but i just need a hint to start writing. Thank you

Answer 1

I did something to similar to this a while ago. The approach I took was to use the solver (as gary's student suggests). I think it was fired from VBA but that's unimportant.

Basically you'd have two input cells per row of data with your variables K and C. Then you need to find the difference (errors) between the values the function produces with the values in the input cells compared to the actual values (I think using errors^2 gives quicker conversion). You then sum the differences in another cell. When running the solver, you ask it to minimise the sum of differences by changing K and C.

Does that makes sense...?