MATLAB: How to normalize rows of a matrix

matrixnormalize

I have a matrix called aefm_1 that is 184 x 5119 where each row indicates a signal vector and each column is a time step and each value in the signal vector indicates amplitude at that time step. I want to write a loop that normalizes each signal vector in the matrix from -1 to 1 based on the maximum amplitude for each row. When I try to use the code below, it outputs only a singal vector of dimensions 1 x 5119. In the end, I want an output that is still 184 x 5119. How do I do that?

for i=1:size(aefm_1,1)

aefm_2 = aefm_1(i,:)./max(abs(aefm_1(i,:)));

end

Best Answer

Kimberley - your code is overwriting the value that was assigned to aefm_2 on the previous iteration

aefm_2 = aefm_1(i,:)./max(abs(aefm_1(i,:)));

You will need to set this variable to be an array with the same dimensions as aefm_1 and then update each row of it. Alternatively, you could probably do this in a single line of code without a loop.

aefm_2 = aefm_1 ./ max(abs(aefm_1), [], 2);

See here for why we add the [] and 2 paramaters as inputs to max.

Related Solutions

MATLAB: How to do normalization of a matrix

You can use the function normalize and specify which dimension you want to normalize.

From the documentation

"N = normalize(A) returns the vectorwise z-score of the data in A with center 0 and standard deviation 1.

If A is a vector, then normalize operates on the entire vector.

If A is a matrix, table, or timetable, then normalize operates on each column of data separately.

If A is a multidimensional array, then normalize operates along the first array dimension whose size does not equal 1. "

MATLAB: How to normalize all the matrices in a loop so that each row sums up to 1

There are two parts to your question - (a) how to normalise each row of a matrix at once, and (b) how to do it independently for each matrix in a cell array.

(a)

use the dot notation to divide each row by the sum of that row

So for a matrix M,

M = M./sum(M,2);     % sum acros the 2nd dimension (column) and do a row-wise division

will normalise each row to sum to 1.

If instead you want to normalise each column, simply:

M = M./sum(M,1);

(b) You can either use a for loop to do the same for each matrix A{jj} of the cell array

for jj=1:N
    A{jj} = A{jj}./sum(A{jj},2);
end

OR use a neat arrayfun to do the same:

A = arrayfun( @(jj) A{jj}./sum(A{jj},2), 1:N , 'UniformOutput', false );

where i use the array fun to loop over 1 to N, setting uniform output to false so my result is also a cell-array. Imagine it like:

output = arrayfun( @jj, func(something), loop over 1 to N, 'UniformOutput', false)

Best Answer

Related Solutions

MATLAB: How to do normalization of a matrix

MATLAB: How to normalize all the matrices in a loop so that each row sums up to 1

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