topic Re: genfit problem about number of parameters in PTC Mathcad
https://community.ptc.com/t5/PTC-Mathcad/genfit-problem-about-number-of-parameters/m-p/700084#M193077
<P>Mathcad often is very sensible with respect to the guess values which will have to be chosen with great care.</P>
<P>You may want to have a look at the eval version of CurveExpert Pro. Even in demo w/o the various export options mode its quite useful for curve fitting. It has a lot of predefined function types which it tries on the data and you may also define your own.</P>Wed, 25 Nov 2020 01:28:10 GMTWerner_E2020-11-25T01:28:10Zgenfit problem about number of parameters
https://community.ptc.com/t5/PTC-Mathcad/genfit-problem-about-number-of-parameters/m-p/700018#M193066
<P>The error message says the number of fitting parameters and guess values must be the same, but they do !!!</P>
<P>Please, take a look to the file attached, this is a short programm.</P>Tue, 24 Nov 2020 17:35:01 GMThttps://community.ptc.com/t5/PTC-Mathcad/genfit-problem-about-number-of-parameters/m-p/700018#M193066jcoolman2020-11-24T17:35:01ZRe: genfit problem about number of parameters
https://community.ptc.com/t5/PTC-Mathcad/genfit-problem-about-number-of-parameters/m-p/700036#M193069
<P>Not exactly sure what you mean by <FONT face="batang,apple gothic"><EM>"The combination of these three functions gives a family of non-asymptotic sigmoid functions"</EM></FONT>. Which kind of "combination"?</P>
<P>If you have a simple additive combination in mind, you would have to do it that way, nut the result sure is not satisfactory (and very sensitive wrt the guess values):</P>
<P><span class="lia-inline-image-display-wrapper lia-image-align-inline" image-alt="Werner_E_0-1606247813739.png" style="width: 556px;"><img src="https://community.ptc.com/t5/image/serverpage/image-id/34091i0D65561016FAEBDF/image-dimensions/556x294?v=v2" width="556" height="294" role="button" title="Werner_E_0-1606247813739.png" alt="Werner_E_0-1606247813739.png" /></span></P>
<P>But if you want to say that you would like to split your curve into three parts and fit a different function type to each part, then you would have to do the splitting yourself and fit three times.</P>
<P> </P>
<P>BTW, Here's a function which seems to fit your data pretty well:</P>
<P><span class="lia-inline-image-display-wrapper lia-image-align-inline" image-alt="Werner_E_1-1606248764584.png" style="width: 400px;"><img src="https://community.ptc.com/t5/image/serverpage/image-id/34092i2B0DA24B73BB2AD3/image-size/medium?v=v2&px=400" role="button" title="Werner_E_1-1606248764584.png" alt="Werner_E_1-1606248764584.png" /></span></P>
<P> </P>
<P> </P>
<DIV id="tinyMceEditorWerner_E_2" class="mceNonEditable lia-copypaste-placeholder"> </DIV>Tue, 24 Nov 2020 20:12:56 GMThttps://community.ptc.com/t5/PTC-Mathcad/genfit-problem-about-number-of-parameters/m-p/700036#M193069Werner_E2020-11-24T20:12:56ZRe: genfit problem about number of parameters
https://community.ptc.com/t5/PTC-Mathcad/genfit-problem-about-number-of-parameters/m-p/700077#M193076
<P>Yeah, I was talking about "linear combinations of functions" , sorry.</P>
<P>Thanks, you helped me to fix this error, now I can fit with genfit.</P>
<P>I think mathcad is not good for fitting points if they are not well close to a mathematical curve, but experimental points are random up and down from such a curve.</P>
<P>I was hopping to fit experimental points to non asymptotic sigmoid curves like this <A href="https://stats.stackexchange.com/questions/398551/logistic-function-with-a-slope-but-no-asymptotes" target="_blank">https://stats.stackexchange.com/questions/398551/logistic-function-with-a-slope-but-no-asymptotes</A></P>
<P>(because some chemical law predicts this) you see there are 5 paramenters, I also added a sixth parameter x0 in this form: instead x I put (x-x0) hopping the fitting process could find the best x0, but the outcome was ugly.</P>
<P>SigmaPlot can fit this without problem (sorry for comparison) but at the moment I haven't this software.</P>
<P>Thank you anyway.</P>Wed, 25 Nov 2020 00:22:19 GMThttps://community.ptc.com/t5/PTC-Mathcad/genfit-problem-about-number-of-parameters/m-p/700077#M193076jcoolman2020-11-25T00:22:19ZRe: genfit problem about number of parameters
https://community.ptc.com/t5/PTC-Mathcad/genfit-problem-about-number-of-parameters/m-p/700084#M193077
<P>Mathcad often is very sensible with respect to the guess values which will have to be chosen with great care.</P>
<P>You may want to have a look at the eval version of CurveExpert Pro. Even in demo w/o the various export options mode its quite useful for curve fitting. It has a lot of predefined function types which it tries on the data and you may also define your own.</P>Wed, 25 Nov 2020 01:28:10 GMThttps://community.ptc.com/t5/PTC-Mathcad/genfit-problem-about-number-of-parameters/m-p/700084#M193077Werner_E2020-11-25T01:28:10ZRe: genfit problem about number of parameters
https://community.ptc.com/t5/PTC-Mathcad/genfit-problem-about-number-of-parameters/m-p/700085#M193078
<P>+1 for CurveFit Pro. One thing I have been using it for lately is reverse engineering a few older nomographs that are used in my type of civil engineering, but for which I cannot find the equations that were used to build them. I extract data points from the curves with a scale, drop them into CurveFit Pro, and find the best fit equation that I can then use in Mathcad, Excel, or one of my programmable HP calculators.</P>Wed, 25 Nov 2020 01:33:42 GMThttps://community.ptc.com/t5/PTC-Mathcad/genfit-problem-about-number-of-parameters/m-p/700085#M193078FredLusk2020-11-25T01:33:42ZRe: genfit problem about number of parameters
https://community.ptc.com/t5/PTC-Mathcad/genfit-problem-about-number-of-parameters/m-p/700188#M193082
<P>Could not find "CurveFit Pro" in a first quick search on the net. Did you mean "CurveExpert Pro" which I mentioned above?</P>Wed, 25 Nov 2020 10:12:05 GMThttps://community.ptc.com/t5/PTC-Mathcad/genfit-problem-about-number-of-parameters/m-p/700188#M193082Werner_E2020-11-25T10:12:05ZRe: genfit problem about number of parameters
https://community.ptc.com/t5/PTC-Mathcad/genfit-problem-about-number-of-parameters/m-p/700300#M193091
<P>Werner...</P>
<P> </P>
<P>You are correct. I brain-freezed the name.</P>
<P> </P>
<P>Fred</P>Wed, 25 Nov 2020 20:31:35 GMThttps://community.ptc.com/t5/PTC-Mathcad/genfit-problem-about-number-of-parameters/m-p/700300#M193091FredLusk2020-11-25T20:31:35Z