Having trouble with feval and function

Question

While I have my function grad as

function g = grad(x)
    g = [4*(x(1)-4)^3 ; 2*x(2)-6 ; 16*(x(3)+5)^3];

end

Why do i have a error message "Not enough input arguments. Error in grad (line 2) g = [4*(x(1)-4)^3 ; 2x(2)-6 ; 16(x(3)+5)^3];" when I try to run the code

x = [4;2;-1];
feval(grad,x)

Any assistance would be appreciated.

Answer 1

When passed as an argument of the feval, the function name should be passed as a string or as a function handle. So:

x = [4;2;-1];
feval("grad", x)

(Notice the quotation marks around the "grad").

Or:

x = [4;2;-1];
feval(@grad, x)