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FanCG1-Visitor
1-Visitor
April 12, 2012
Solved

a question of parameter fitting in an experiment

  • April 12, 2012
  • 16 replies
  • 7192 views

during recent experiments, I got some data like following figure.

y is the operating parameter of my experiment and z is what I wanna measure. x varies from 0 to 1

usually, such kind of data are usually fitted by an equation that looks like "z=F(y) exp[Σαi x^n]"or something others like this.

I tried to do this in mathcad twicely, but failed totally at last.

could anyone please help me solving the problem?

data fitting.JPG

Best answer by RichardJ

Here's a general way to fit multidimensional data. It will work with any number of dimensions and any objective function, and does not need multidfit.

You need a different objective function to the one you specified though. That sum of exponentials cannot fit the shape of your curves in the x direction. You should be able to edit this worksheet easily enough to change that though.

16 replies

VladimirN24-Ruby IV
24-Ruby IV
April 13, 2012

Fan CG wrote:

...I tried to do this in mathcad twicely, but failed totally at last...

Could you attach your Mathcad worksheet?

Raiko17-Peridot
17-Peridot
April 13, 2012

Hello,

maybe this sheet helps. Did it with MC 15 on a Win 7 (64 bit) machine

Raiko

FanCG1-VisitorAuthor
1-Visitor
April 13, 2012

I tried this method at first, but later I found that I actually needed a 2D fitting result. The attached solution can only tell me the relationship between "x" and "z", but none of the business of "y". Maybe I need to resortma to matlab.

thanks for your help

Fred_Kohlhepp23-Emerald I
23-Emerald I
April 13, 2012

Fan CG wrote:

I tried this method at first, but later I found that I actually needed a 2D fitting result. The attached solution can only tell me the relationship between "x" and "z", but none of the business of "y". Maybe I need to resortma to matlab.

Perish the thought!

You can do regress in two dimensions:

HarveyHensley12-Amethyst
12-Amethyst
April 13, 2012

Here's another approach.

    FanCG1-VisitorAuthor
    1-Visitor
    April 13, 2012

    Thank you Harvey

    your idea is very close to mine, I failed at using minimize function.

    but I m not sure which verion of mathcad you are using.

    coz I can only read the first part of your solution

    when you began to convert data to multidfit form for final fit of C, it was reported by my mathcad14 that "multdfit" is an undefined fuction.

    I will study your solution tomorrow morning, now it is too late, I have to throw myself onto my bed

    HarveyHensley12-Amethyst
    12-Amethyst
    April 13, 2012

    I'm using version 15. I tried sending a pdf file so you could at least see the results, but the upload seemed to stall.

    Instead, here's a snip of the results.Capture.JPG

      FanCG1-VisitorAuthor
      1-Visitor
      April 16, 2012

      thanks a lot for both of you, and I will try to improve my job. I will show my results if there are any more improvements

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