Why are guess values needed in MathCAD for power and exponential regressions? Excel doesn't need them. Attached is a mathcad and excel document that gets me nothing but frustrated. All I have is x and y values that I am passing into both MathCAD and excel. MathCAD can't find the a,b and c values to satisfy the regressions, even when I give it the same ones I found using Excel. I even graphed the excel values in Mathcad and they worked. Why doesn't Mathcad find the coefficient values of the regression?
Origin is superb on some aspects. It was no sweat fitting your data. By the way, some of the data are in error. In such case, it's good practice to eliminate the bad ones. If your project was " real life " then use it. I think this the true approximation .
Origin is superb on some aspects. It was no sweat fitting your data. By the way, some of the data are in error. In such case, it's good practice to eliminate the bad ones. If your project was " real life " then use it. I think this is the true approximation .
The approximation I gave yesterday, was extracted using Origin. This software does not require initial guess values. By default it varies each parameter. But the number of iterates may be specified. The first approximation was with 1 iterate, the second one used 10 iterates.
You are right Hubert. Since I have Mathcad, I rarely use Origin. You like it too ! So nice graphs. Combining Origin and Mathcad, would be near perfect. I tried Origin for one of my favorite rational fraction approximation, then it has no guess values because there is no model. It comes close to exact answer, just by itself, and there are 3 coefficients. I do the same with Mathcad, but in steps. It could be programmed in Mathcad, but I'm not skilled at that. As a matter of facts, for certain type of curves, I can generate an excellent P(x)/Q(x), in simple steps. Why these big guns: Mathcad, Mathematica, Mathlab... are so poor about approximating functions ??? Can you imagine, none of them included the Thi�l� Continued fraction...F. If you read me, Danish Collab, I will make a file for you. Because Thi�l� is Danish. And such a great tool, you must have it. I have many sheets, using Thi�l�. Yes Sir !
I copied the page that remained in my mail box. The latest version is 6.1. In 6.1, you will find added functionalities. As such, it's the same software. Their forum is well, well, well supported. Superb companionship with Excel. Origin is a spread sheet type too. But not very convenient writing equations in script format. I have not tried it with Mathematica. Origin is a very interesting gear. I believe < $ 1000. Your link is at the bottom of the page. Bob Sullivan will gladly consider your quest. I think their latest link is: http://www.origin.lab
Let me know if you have difficulties.
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Sorry. But it is the chat about Mathcad. I know a lot of software for regression analyze (best than Excel, Origin etc). I can tell about this software, but thru e-mail. Valery Ochkov http://twt.mpei.ac.ru/ochkov
well, I second Valery, about this forum rather belonging to Mathcad, regarding the Origin-ads. Yet a discussion about other programs and comparing their capabilities and limitations to Mathcad is useful too! 😉
One final info about Origin: it�s great for displaying and analyzing data. The manufacturer is OriginLab (formerly known as Microcal), Origin6.1 is their most recent version (I always would recommend the PRO) and their website is www.originlab.com . They provide Demo-versions.
It would be great, to have some examples, which combine Mathcad with Origin (should be possible with scripting, but I am no OLE- or VB-wizard).
Thanks Valery and Hubert. I got used to approximate functions through my profession in Instrumentation. My tools are quite simple: Polynomials, Thi�l� (which I love so much and complements so nicely Lagrange). I have a short library of remarkable functions. In complement I wish I would have:
1. a tool to extract the 'an' coefficients for ChebyShev ( input [x : y ] and return the final an ....something like the approximation of Neperian Log. We have a case in cryogenic semiconductors) 2. For certain type of curve fitting, I have my own unpublished tool to extract rational fractions: P(x)/Q(x). But I don't have a generalized method.
3. The issue is to have Mathcad execute in simple modules. My Fortran is so far away.
Sorry! But I does not say that the *visible* guess values are the best guess values. I only say that we can use the visualization for solve this task. See my messages about this subject in Probability & Statistic Forum too. Valery Ochkov http://twt.mpei.ac.ru/ochkov
All these people looking at this and coming up with fancy theories as to the problem. An no one bothering to look at the actual code and notice the the on error construction is coded backwards, so that the fitting command would only be executed if the evaluation of the guess values fail (not likely, as the guess values are coded as constants.