How can I perform matrix calculations within the own matrix?

Hi,

I have a 9x612 matrix (A). It consists of 102 variables measured 6 times each (612 columns), in 9 different situations (9 rows). I would like to normalize each repetition to its first one (i.e. A(:,1:6) normalised to A(:,1); A(:,7:12) normalised to A(:,7), etc.

How could I perform these calculations using a for loop?

This is what I have been trying so far without success:

A_normalised = zeros(size(A));
for ii = 1:6:length(A);
    for kk = ii+1:ii+5;
        A_normalised(:,:) = ((A(:,kk).*100)./A(:,ii));
    end
end

However this leads to the error: "Assignment has fewer non-singleton rhs dimensions than non-singleton subscripts"

Please, find attached a matrix example.

Answer 1

[Antonio Morales]

A_normalised = zeros(size(A));
for ii = 1:6:length(A)
    for kk = ii:ii+5
        A_normalised(:,kk) = (A(:,kk).*100)./ A(:,ii)-100;
    end
end

Answer 2

[Greg]

The right hand side (rhs) evaluates to a column. The left hand side (lhs) references the entire matrix (612 columns). You can't stick a single column into 612 separate columns (with that type of index notation).

On the lhs, specify the proper column to store the result in. (Hint: it's probably one of your loop index variables).

Also, I would use repmat, repelem, bsxfun, or other similar function to remove both loops entirely.

[Antonio Morales]

Thanks. This is now giving me what I was looking for:

A_normalised = zeros(size(A));
for ii = 1:6:length(A)
    for kk = ii:ii+5
        A_normalised(:,kk) = (A(:,kk).*100)./ A(:,ii)-100;
    end
end