How to fix my my convolution function?

Hi, my teacher wants us to make a convolution function instead of using matlabs and this is what i have

x=[1 2 3 4] y=[1 2 3 4]

function P = MyConv1(x,y)

p = length(x); q = length(y);

for n = 1:p+q-1

     for k = 1:n
        P(n) = [sum(x(k)*y(n-k))];
    end
end

however i get this error:

Attempted to access y(0); index must be a positive integer or logical.

Error in MyConv1 (line 11) P(n) = [sum(x(k)*y(n-k))];

someone please help me figure out what the issue is

Answer 1

[Image Analyst]

Then add 1. n-k is 0 and MATLAB doesn't allow a zero index. Try n-k+1.

[Andrew]

that did not work. And the formula for convolution states n-k so that is why I kept that.

this is the error with that

Attempted to access y(5); index out of bounds because numel(y)=4.

Error in MyConv1 (line 11) P(n) = [sum(x(k)*y(n-k+1))];

[Image Analyst]

Just write the arrays down on paper. Slide them across and see what gets multiplied. It's not that hard to see what to do if you do that. If you really can't figure it out, come back.