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rsulwinski1-Visitor
1-Visitor
March 7, 2017
Solved

Calculating a derivative of an array

  • March 7, 2017
  • 6 replies
  • 5336 views

Hello,

I would like to know if it is possible to calculate a derivative of an array in Mathcad without fitting a function to the data set. A have an expression of a form: sigma(x,y):=A*F,x(x,y), where A is a constant, and F(x,y) is a function of x and y which is defined with a data set/array (data imported from Finite Element Analysis). I would like to calculate a derivative of F(x,y) with respect to x.  

Best regards

Rafal

Best answer by -MFra-

Hi Rafal,

You should create a program that performs the following operation:

derivata approssimata di una funzione rispetto a x.jpg

For Rafal.jpg

Regards

F. M.

6 replies

F
Fred_Kohlhepp23-Emerald I
23-Emerald I
March 7, 2017

If you have a set of discrete points finite difference techniques will give you an approximation of the derivative.

There are fitting functions in Mathcad, numerous options.  To get a true derivative you need a function.  (I believe.)

    R
    rsulwinski1-VisitorAuthor
    1-Visitor
    March 8, 2017

    You are right Fred. Finite difference is one option. When it comes to function fitting, the Mathcad quick sheet "Using Regress: Multivariate Regression" contains a procedure on how to fit a n-dimensional data to a higher order polynomial. 

    -
    -MFra-21-Topaz IIAnswer
    21-Topaz II
    March 8, 2017

    Hi Rafal,

    You should create a program that performs the following operation:

    derivata approssimata di una funzione rispetto a x.jpg

    For Rafal.jpg

    Regards

    F. M.

      R
      rsulwinski1-VisitorAuthor
      1-Visitor
      March 8, 2017

      Thank you very much! This is exactly was I was looking for! It is quite a procedure, very impressive. The program will allow me to calculate a derivative of the solution data imported from FEA.

      Best regards

      Rafal

      L
      LucMeekes23-Emerald IV
      23-Emerald IV
      March 8, 2017

      Does this help?

      And very simple:

      The parabola gives a straight line, the straight line gives a constant.

      Success!

      Luc

        R
        rsulwinski1-VisitorAuthor
        1-Visitor
        March 8, 2017

        Hi Luc,

        Thank you for your reply. Your program indeed works, but it can only deal with a function of one variable F(x). My problem was defined as a function of two variables F(x,y).

        F.M. provided a program can deal with a function of two variables, therefore I have selected his answer as the correct one. 

        Best regards

        Rafal

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