passing function handle to separate function m-file error

Hi,

I have a function (function-1) which passes a function handle of the form:

fhandle = @fun; % step-1

to a function in a separate m-file (function-2). I invoke this function handle in function-2 using:

res = feval(fhandle, ...); % step-2

where the function in 'fhandle' is defined as a separate non-nested function within the function-2 m-file (function-2-1). However, this gives the following error:

"Undefined function 'fun' for input arguments of type 'double'."

I have also tried invoking the function handle directly, which also gives the same error:

 res = fhandle(...); % step-2-v.2

This is odd, as if I go into function-2 in debug mode and re-enter the code in step-1 again, and then re-run step-2 and step-2-v.2, it seems to evaluate the function just fine. A work-around I have found is by defining the function handle as a string:

 fhandle = 'fun'; % step-1-v.2

which seems to work fine. However, I have read that it is better practice to use the function handle form @, rather than passing a string. Could this be a bug or am I missing something?

Thanks

Answer 1

[Jan]

Thjis is the expected behavior. "fhandle = @fun" runs inside the function 1. There the functions, which are defined inside function 2, are unknown and therefore @fun is invalid. Of course @fun is valid, when you run the debugger and are inside function 2 already.

Summary: You can create function handles only to functions, which are currently visible.

Solution: Use another method to tell function 2 which subfunction should be used:

function [out] = function2(Fcn, Data)
% Fun: String to specify the subfunction:
switch lower(Fcn)
  case 'fcn1'
    fhandle = @fcn1;
  case 'fcn2'
    fhandle = @fcn2;
  otherwise
    error('Unknown function: %s', Fcn);
end

plot(1:10, fhandle(1:10));
end

function y = fcn1(x)
y = sin(x);
end

function y = fcn2(x)
y = cos(x);
end

Alternatively:

Create M-files for the sub-functions. Then their handles are visible from anywhere.

[Rogge Zheng]

Thank you, great explanation, solved my problem！