MATLAB: Looping through two matrices with IF statement

forif

[EDIT: Mon May 23 16:36:16 UTC 2011 – Reformat – MKF]
Hello, I am having problems with my for loop statement (see code at bottom). I'm trying to overwrite a zeros matrix (A) with 1's if it meets certain criteria from another matrix (M). It essentially needs to look at M(:,1) and put ones in each row of A (for each numatch) according to the if conditions. Instead of putting ones in the right place, it puts in all ones up to the last numatch row. Here is the code:
%creates A
nx = 5;
ny = 6;
nullnx = zeros(nx,2);
nullny = zeros(ny,2);
nullnx(:,1)=[1:nx];
nullny(:,2)=[1:ny];
if nx >= ny;
    numatch = nx;
else
    numatch = ny;
end;
if nx >= ny;
    x = repmat(nullnx(:,1),nx,1);
    matchx = sort(x);
    mx = cat(2, matchx, x);
else
    x = repmat(nullny(:,2),ny,1);
    matchx = sort(x);
    mx = cat(2,matchx,x);
end;
M = [nullnx;nullny;mx];
A = zeros(nx+ny+numatch,nx+ny+numatch);
%here is where I need help
for i = 1:numatch;
    for a = 1:length(M);
        for b = 1:length(A);
            if M(a, 1)== i;
                A(i,b)=1;
            end;
        end;
    end;
end;
Any help is most appreciated

Best Answer

Your code is doing exactly what you describe that it should do, that is it: "looks at M(:,1) and put ones in each row of A (for each numatch) according to the if condition."
Now is it the case that you need a different IF condition? If so, please show a simple example of input and expected output.
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EDIT In response to your comment below.
Does this do it?
for ii = 1:numatch;
    A(ii,:) = M(:,1)==ii;
end;
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