How to skip elements of matrix in a loop?

Hi

If I have a matrix defined as:

V = zeros(20,20);

%sides at 1,-1

V(1:21,1) = 1;

V(1:21,21) = -1;

V(1:21,2:20) = 2;

%zero potential triangle

V(14,8:13) = 0;

V(13,9:13) = 0;

V(12,10:13) = 0;

V(11,11:13) = 0;

V(10,12:13) = 0;

V(9,13:13) = 0;

(two metal plates with v=1 and v=-1 and a triangle in the middle v=0)

I am implementing the jacobi method by:

for j=2:column_size-1;

for i=2:row_size-1;

if V(i,j)~=1 & V(i,j)~=-1 & V(i,j)~=0 %update

V_new(i,j) = (V(i-1,j)+V(i+1,j)+V(i,j-1)+V(i,j+1))/4;

delta_V_new = delta_V_new+abs(V_new(i,j)-V(i,j));

else

V_new(i,j) = V(i,j); %keep initial conditions

end;

end;

end;

The loop is not converging properly. I want to keep the same boundary conditions..is there a way to skip the elements of the triangle in the middle without using the if statement? I am fine with using the if statementfor the 1 and -1

Thanks

Answer 1

[Image Analyst]

Just make up a mask with true or false where you want it to process, or skip. Then

for j=2:column_size-1;
    for i=2:row_size-1;
        if ~mask(i, j)
            % Mask is false here, so skip rest of the loop.
            continue; 
        end
        % Else mask is true, so do the rest of the loop.
    end
end

The "false" region(s) shape mask can be whatever shape you want, but the overall size should be row_size by column_size.