Setting variable to zero with conditional statement?

I'm writing a for loop which runs through values and sometimes the element that the loop selects is outwith the vector length.

For example, say I have a vector of 10 entries and the loop asks for the 11 "th" entry it doesn't exist so I get an error.

How do I put this in the code with an if statement? I want the code to go like:

%the loop selects y(n)

if n>10 then set y(n) = 0

else y(n) = y(n)

Sorry if it's unclear, I'm sure it's a simple fix?

[Jose Marques]

Could you post your entire code? So we can help you better

[matlabkid602]

shift = k-n;

      if shift <1 || shift >21

          y(shift) = 0;
      end

Answer 1

[Walter Roberson]

if n>length(y); y(n) = 0; end

[matlabkid602]

Subscript indices must either be real positive integers or logicals.

n can be positive or negative. This doesn't work.

How can this be done on Matlab?

[Walter Roberson]

If I understand correctly, for negative shift you would like to set array locations with negative indices? That is not permitted in MATLAB. Do you want negative shift to be interpreted as starting from the maximum value, with n = -1 being interpreted the same as y(end) and n = -2 being interpreted the same as y(end-1) ?

[matlabkid602]

If I choose k such that somewhere during the loop "shift" becomes negative, or greater than the length of y, I want y(shift) = 0.

I'm solving ODE's with the loop and need this condition.