Adding numbers to specific matrix index.

i want to fill in a 100x100 matrix using a nested for loop. However for each ’i’ row there will only be 3 ‘j’ columns with nonzero numbers. Also i want leave the first and last row all zeros. This is what ive tried before and its not working. what am i doing wrong?

A = zeros(100,100);
h = 1;
for i = 2:99;
    for j = 2:99;
        A(i, j+1) = ((1/h) + i); 
        A(i, j) = (-2/h);
        A(i, j-1) = ((1/h) - i);
    end
end
%so after one iteration i would have the values at the given indices
% %A(2,3) = 3
%A(2,2)=-2
%A(2,1)=-1

Answer 1

[Geoff Hayes]

However for each ’i’ row there will only be 3 ‘j’ columns with nonzero numbers How do you determine which three columns of the ith row are non-zero? In your above example, for the second row, the first three elements are non-zero. Does this mean that in the third row, the 2-4 columns are non-zero? In which case you would do something like

A = zeros(100,100);
h = 1;
for i = 2:99;
    A(i, i+1) = ((1/h) + i); 
    A(i, i) = (-2/h);
    A(i, i-1) = ((1/h) - i);
end

Or are you trying to do something else?

[Mr.Tentacles]

yes this works thanks you