get number of output arguments of a function handle

Question

Alwin Förster 2022-1-4

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1622150-get-number-of-output-arguments-of-a-function-handle

回答： Steven Lord 2022-1-4

采纳的回答： Steven Lord

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

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Answer 1

Steven Lord 2022-1-4

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1622150-get-number-of-output-arguments-of-a-function-handle#answer_867870

在 MATLAB Online 中打开

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