get number of output arguments of a function handle

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Is there a better way to get the number of output arguments (should be one or two) of a function handle than this:
a = 1;
b = 2;
x0 = 0;
fun = @(x) function_file(x,a,b);
try
[f1,f2] = fun(x0);
nout = 2;
catch
nout = 1;
end
It should also work if the function is:
fun = @(x) a*x.^b;
Therefore catching the name 'function_file' using functions(fun) and then use nargout('function_file') is not an option.
Thanks in advance!
Alwin

Accepted Answer

Steven Lord
Steven Lord on 4 Jan 2022
Calling nargout on the function handle itself may give an answer.
nargout(@sin) % The sin function returns 1 output
ans = 1
But it may not be possible to tell from the function handle with how many outputs it can be called.
nargout(@size) % Can be called with an arbitrary number of output arguments
ans = -1
I believe calling nargout on an anonymous functions always returns -1 because MATLAB can't tell with how many output arguments the code that makes up the body of the anonymous function can be called until you actually call it.
f = @(x) svd(x);
nargout(f)
ans = -1
A = magic(4);
% Call f with 1 output
s = f(A)
s = 4×1
34.0000 17.8885 4.4721 0.0000
% Call f with three outputs
[u, s, v] = f(A)
u = 4×4
-0.5000 0.6708 0.5000 -0.2236 -0.5000 -0.2236 -0.5000 -0.6708 -0.5000 0.2236 -0.5000 0.6708 -0.5000 -0.6708 0.5000 0.2236
s = 4×4
34.0000 0 0 0 0 17.8885 0 0 0 0 4.4721 0 0 0 0 0.0000
v = 4×4
-0.5000 0.5000 0.6708 -0.2236 -0.5000 -0.5000 -0.2236 -0.6708 -0.5000 -0.5000 0.2236 0.6708 -0.5000 0.5000 -0.6708 0.2236

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