Calculating a derivative of an array

[rsulwinski]

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

[Fred_Kohlhepp]

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.)

[rsulwinski]

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- · Accepted solution]

Hi Rafal,

You should create a program that performs the following operation:

Regards

F. M.

[rsulwinski]

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

[LucMeekes]

Does this help?

And very simple:

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

Success!

Luc

[rsulwinski]

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