Evaluate function handle with "for"

I want to write a code to obtain the partial derivates of a function R^n ->R given by the user. For that, the parameters in which I evaluate the function change according to the variable that is being derivated.

I thought about using a FOR loop, but I don't know how to write the code so it will chance the values where the function is evaluated according to the variable.

For example, the code for the first two varibles would be

parcial_1 = (feval(f,x0+h,y0)-feval(f,x0-h,y0))/(2*h);

parcial_2 = (feval(f,x0,y0+h)-feval(f,x0,y0-h))/(2*h);

The full code I have is this

x0 = 2;
y0=2;
h = 0.01;

f=input('Input the function:  ');
num_variables=nargin(f);
disp(num_variables);
for i=1:num_variables
    parcial_i=(feval(f,x0+h,y0)-feval(f,x0-h,y0))/(2*h);
end

Answer 1

[Walter Roberson]

f=input('Input the function:  ');
num_variables=nargin(f);

varvals = {2, 2, zeros(1, num_variables-2)};

for i = 1 : num_variables
    t1 = varvals; t2 = varvals;
    t1{i} = t1{i} + h; t2{i} = t2{i} - h;
    partial{i} = (feval(f, t1{:}) - evalf(f, t2{:}))/(2*h);
end