how i correct error in Matlab

I receice this error

Attempt to reference field of non-structure array

Error in perturb_method (line 136)

[j,k]=find(pop(i).mat.p==x)

[Rik]

Clearly you read Jan's answer below (as you edited the question). Did his suggestion solve the issue?

[dalel amami]

not yet, i only rectify the syntax error, pop is a population of structred matix (mat) i want to knew the indices of a specific elemnet in the part p of matrix mat, how can i process please?

[Jan]

I've explained already how to use the debugger to find out, what the cause of the error message is. If pop(i).mat is not a truct, you cannot access a not existing field p . Without seeing your code and the data, it is impossible to guess, what you want to do instead.

What does Matlab show you, when it stops at the error message in debug mode, for:

class(pop)
class(pop(i).mat)

Answer 1

[Jan]

The error message means, that either pop or pop(i).mat is not a struct, such that you cannot access a field using the dot.

Check this with the debugger. Type this in the command window:

dbstop if error

Then run your code again until it stops at the error. Now check the classes:

class(pop)
class(pop(i).mat)

But I'd expect another error message:

find(pop(i).mat.p=x)
%                ^

Inside the FIND command, you should use the == operator for the elementwise comparison, not = for assining a value.