MATLAB: How to determine the size of an array of functions?

array of functions;

F = @(x1,x2) [(4*x1^2-20*x1+x2^2/4+8) ; (x1*x2/2+2*x1-5*x2+8)]
J = @(x1,x2) [(8*x1-20)  (x2/2) ; (x2/2+2)  (x1/5-5)]
x0 = [ 1 2 3 4 ];
tol = 10^-5;
A = nargin(F);
B = nargin(J);
I would like to find the size of F & J because i will use those as inputs to my function and they will not be known. Something like:
[C D]=size(F)
[G H]=size(J)
would be excellent if it worked. At first I thought matlab didn't like doing the anonymous matrix thing I'm trying, but it evaluates the functions just fine if given an input like:
F(0,0)
will output:
[8 ; 8]
as it should.
So i tried evaluating the functions with 'A' and 'B' number of zeros, but didn't have much luck in figuring that out as an array is not what the functions input.
Any help would be greatly appreciated!

Best Answer

There is no general solution because the size of the output can depend on the inputs. Consider:
>> fun = @(x)x+2;
>> fun(1)
ans =  3
>> fun(1:5)
ans =
   3   4   5   6   7
>> foo = @(x)zeros(1,x);
>> foo(2)
ans =
   0   0
>> foo(7)
ans =
   0   0   0   0   0   0   0
Even then it will only return the size for those given inputs. Consider:
>> baz = @(x,y)[x;y];
>> baz(3,2)
ans =
   3
   2
>> baz(3:6,2:5)
ans =
   3   4   5   6
   2   3   4   5
>> baz([1;2;3],4)
ans =
   1
   2
   3
   4
What size would you describe baz as returning?
The only robust solution is to call the functions with the inputs of the required size and measure the output size:
>> J = @(x1,x2) [(8*x1-20)  (x2/2) ; (x2/2+2)  (x1/5-5)];
>> size(J(0,0))
ans =
   2   2
>> size(J(1:3,1:3))
ans =
   2   6
Note how the size of the output from your function depends on the inputs!
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