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nanay1-Visitor
1-Visitor
March 1, 2013
Question

Exponential Fit Curve Help

  • March 1, 2013
  • 10 replies
  • 4200 views

Hello,

I am trying to create a best-fit curve for a data set. I have imported two excelsheets containg the data into Mathcad. Each excel contains 1066 intergers. I have plotted them using the x-yplot functionality. The plot appears to follow an exponential projection. So, I tried to obtain exponential fit curve using the expfit() function. However, the fit function that I obtained is not correct, because it does not fit the data.

Please advise what I shoulddo to obtain the proper exponential fit curve.

10 replies

RichardJ19-Tanzanite
19-Tanzanite
March 1, 2013

Please post a worksheet with the data. We can show you how to perform a generalized fit that can be applied to any function (but I don't know what that function might be without seeing the data).

nanay1-VisitorAuthor
1-Visitor
March 1, 2013

Could you show me how to plot an expfit() function first . I am trying to plot it in MathCAD.

RichardJ19-Tanzanite
19-Tanzanite
March 1, 2013

OK, but I can't plot an expfit function if I don't have data to fit it to

MichaelH1-Visitor
1-Visitor
March 1, 2013

Have you read the Mathcad Help files on using that function and curve fitting in general?

ValeryOchkov24-Ruby IV
24-Ruby IV
March 1, 2013

May be this help you:

http://twt.mpei.ac.ru/ochkov/car/c_e.html

jkowalski1-Visitor
1-Visitor
March 1, 2013

May be this help you: See attach.

nanay1-VisitorAuthor
1-Visitor
March 5, 2013

Hello Jan Kowalski,

Thanks for sending me your sample mathcad files. They have been very helpful.

Now, I am trying to come up with a correlation coefficient associated with the curve fits. I tried using the function corr(A,B), as explained in the Mathcad Help site. However, I am not sure if I am using this fucntion correctly. How do I link the corr function with the fit curve? Are the varibable A, B supposed to be the raw data, or should I use the data from the curve fit? Please explain.

Werner_E
Werner_E25-Diamond I
25-Diamond I
March 5, 2013

It would be time you begin attaching worksheets, don't you think so, too?

Are the varibable A, B supposed to be the raw data, or should I use the data from the curve fit?

Both! As you want to compare the original data (Y) to the fit data you get by the derived function H, you have to throw both into the corr function. First you have to create an apprpriate vector of fit values.

In lack of a sheet from yours I have taken one of the sheet Jan has provided to demonstrate.

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