Curve fitting of a complex function

[Gigiont]

Hello,
I'm trying to fit the imaginary component of an electrical impedance as a function of the real component. Both depend on frequency and I don't see how to express explicitly the imaginary component as a function of the real one.
To do the fit I tried to use a solve block and minimize the residuals for both real and imaginary parts but the result is not that good. Also all the parameters' values need to be positive. I understand that this may not give the best fit, but why MathCad ignores the constraint "Lsc>0"?
I there a better way to fit Im(Re, parameters)?
Thanks,
Gigi

[ptc-1368288]

On 4/22/2010 8:30:33 AM, KristjanLaes wrote:
>These data that will be posted
>here, are the best at the
>moment.
>This switching trouble
>remains, but this seems to be
>a specific trouble of the
>device used. I have heard many
>complaints from many people in
>connection with this.
>KL
_______________________________

Will look at it tonight, now you start trusting "Doctor data" !

Jean

[ptc-1368288]

Attached a good fit, done last night.
Since several months the web collab is not accessible between about 20:00 an 02 , "Web site found, waiting for reply". Whoever is paying $ for the web service pays 6 extra hours, not every day but some days it's more than 6 hours.

jmG

[AlvaroDíaz]

On 4/22/2010 8:30:33 AM, KristjanLaes wrote:

>These data that will be posted here, are the best at the moment.

Done, again with the same schema, just adding some few brute force, just after some few brute words and just because it's nothing easy guessing for six variables.

At the end, a nice combination of montecarlo algorithms, improving error detection, range domain restriction and a adequate handling of complex values to setup a minerr searching for curve fitting problems.

It's weekend and can't check it in mathcad 14.

Regards. Alvaro.

[ptc-1368288]

On 4/21/2010 12:42:49 PM, KristjanLaes wrote:
>hello jmG,
...
>At higher frequencies (around
>100 kHz) the device makes some
>noise like switching and three
>subsequent measurement points
>go out from the smooth trace.
>No cure for that yet.
>
>KL
________________________________

There is more than the kids hard to manage !
Your equipment seems to show numerical instability. This is in conclusion that I get an extraordinary good fit by removing the last two points, but can't reproduce by lack of digits because the X's variate has too large magnitude. The proof is clear like the day if the data set is stripped from the last two values and scaled 0 ... 1

jmG