Answer to my question by skogsgurra
Answer to my question by skogsgurra
(OP)
Hi Skogsgurra
your answer does not really help. Of course I do know that impedances are normally complex.
But assume I am calculating the complex impedance of an RC-circuit. The parameters of R and C will be real. If I then use the complex impedance of the RC-circuit thus obtained as "data" to be fitted, the mcd fitting procedure should find the parameters I originally used and they should be REAL. However, this is only the case if the guess values are already very close to the original values.
This causes problems if I want to apply the fitting procedure to actually measured data.
your answer does not really help. Of course I do know that impedances are normally complex.
But assume I am calculating the complex impedance of an RC-circuit. The parameters of R and C will be real. If I then use the complex impedance of the RC-circuit thus obtained as "data" to be fitted, the mcd fitting procedure should find the parameters I originally used and they should be REAL. However, this is only the case if the guess values are already very close to the original values.
This causes problems if I want to apply the fitting procedure to actually measured data.





RE: Answer to my question by skogsgurra
I still do not see your problem. You can make up any complex impedance from real components - even negative impedances can be built.
I think that it is a bad idea to start a new thread. We should keep this discussion in the original thread.
RE: Answer to my question by skogsgurra
I surely know that one can make complex impedances from real components. My only problem was to tell mathcad not to use complex fitting values instead of real ones for I always obtained complex solutions which might be correct from a mathematical point of view, but not from a physical.
I have solved this problem now.
RE: Answer to my question by skogsgurra
Numerical fitting, by its very nature, is imprecise. However, if you apply the constraints that R and C >0, it should force the solver to dump any complex solutions.
TTFN