how to ignore an index error?

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Laura Alvarez 2019-12-14

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编辑： Laura Alvarez 2019-12-14

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!

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dpb 2019-12-14

编辑：dpb 2019-12-14

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...

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Answer 1

dpb 2019-12-14

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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