how to ignore an index error?

I have this code and I want to ignore the error when the index exceeds array bounds or when they are 0.

for j=1:N
    for i=1:N
        u(i,j)=(c(i,j)+u(i-1,j)+u(i+1,j)+u(i,j-1)+u(i,j+1))/4
    end
end

I just want to ignore u(0, j), u(N + 1, j), u(i, 0) and u(i, N + 1) or assign them the value 0.

Thank you so much!

[dpb]

There is no 0-index array element so assigning it any value, zero or not, is out of the question.

You could put the expression in a try...catch...end construct but reconstructing the expression to maintain arrays in bounds would be the better solution.

filter2() possibly would be of use here altho the expression appears somewhat unusual with five terms dividing by four...

Answer 1

[dpb]

H=[0 1 0;1 0 1; 0 1 0];                                          % filter coefficients
u(2:end-1,2:end-1)=(c(2:end-1,2:end-1)+filter2(H,u,'valid'))/4;  % apply filtered u to c