There is no problem with how you are calling the local function.
However there are several basic problems with the function itself:
function radius = r(x) % you do not use variable x anywhere in your function
SA = 4*pi*r^.2; % variable r is undefined, r is a recursive function call
V = (4/3)*pi*r^.3; % variable r is undefined, r is a recursive function call
radius = ??? % You need to define the output variable
end
The main problem is that you think you are using a variable r, but in fact you are calling the function recursively.
Note that both SA and V are completely unused. I strongly recommend that you avoid using one-letter function names.
See the examples here: https://www.mathworks.com/help/matlab/ref/function.html
