How to define functions in MATLAB.

while writing the code

ff='testfunction';
cost=feval(ff,par);

I got the error undefined function testfunction for input arguments of type double.

Answer 1

[Image Analyst]

You need to do this:

function results = testfunction(ff, par)
cost=feval(ff,par);
results = ..... whatever, more code to assign results.

and save it as testfunction.m.