Mathematical Function as Matlab-Function Input

Hello Everybody!

I have a probably pretty easy to answer question, but I am just not getting to it. How can I tell Matlab to use a mathematical function as an input argument?

To make clear what I mean a very simple example:

function [df] = derivate(y)
x=-20:20;
df=diff(y);
end

If I try to run this now with any kind of function like 3*x+5, Matlab tells me x wasn't defined. Can you tell me my mistake?

Thanks in advance!!!

Answer 1

[Walter Roberson]

You need the symbolic toolbox in order to do this, and you need to declare your free variable with either a sym() or syms() call.

Please also note that you cannot take the derivative of a mathematical function over a range.

If you are trying to do numeric derivatives then you should recode as something like:

function df = derivate(f)
  x = -20:20;
  df = diff(f(x));
end

and you would then call it with a function handle, such as calling

derivate(@(x) 3*x+5)

[Ninja Katja]

Function Handle - that's the thing I was looking for! Thank you! :-)