MatLab: identical function gets two different results

Question

I see the following behavior in 2013a and 2014a on Windows computers:

Someone sends me a .mat file. In this file, a function fi(th, beta) is defined. On the command line I call fi for two values (actually beta is a matrix). Then, I click "edit value" for fi and don't change anything. Then, when I call fi(th, beta) again I get a completely different value.

How can this be? How can I tell what is the "correct" value?

Answer 1

The reason behind your issue is that when clicking edit value on a function handle, it gets updated. In your function, D is used, which was a variable during creation of the function handle. Suppose D now has another value, fi will use the new value after pressing edit value . Let me give you an example:

>> k = 2;
>> f = @(x)k*x;
>> f(4)

ans =

     8

>> k = 4;
>> f(4)

ans =

     8

In this example, k is changed after f is defined. However, f will have its original definition. When I use edit value and don't change anything, it will nevertheless use the new value of k .

>> f % only to show the function has not changed

f = 

    @(x)k*x

>> f(4)

ans =

    16

I hope this clearifies your problem.

Your question regarding the correct value thus depends on the values and function handles used inside the function handle.