invalid argument, expecting an arithmetical expression

Mingyu Yang wrote: Thanks a lot for the screenshot. Let me tell you more about my goal please. I want to get the symbolic result of the real and imaginary parts in this worksheet and then get another set of real and imaginary parts in another worksheet. These two set of symbolic expression would be equal to each other, therefore I got two equations with two unknowns(Rbot&Ctop). I hope I could solve Rbot & Ctop in this way.........But it seems that the expressions are kinda intimidating......Do you think this is feasible?

So at the end you are only interested in a numeric solution for Rbot and Ctop? Then I guess you should be able to succeed. You won't need any symbolic calculations at all to do so. Get rid of all symbolic evaluations and just leave the functions as you had them defined. I guess you will have similar functions from your second sheet. Merge both sheet into one and take care to avoid identical fuctcion or variable names if yoo don't mean the same.

Then provide guess values for Rbot and Ctop and setup a numeric solve block with your two equations (Re(Vfbl(Rbot,Ctop))=Re(Otherfunction(Rbot,Ctop)), etc.)

Edit: See attached sheet.