divide each column of an array by its norm of the column

Question

M 2022-4-9

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1692570-divide-each-column-of-an-array-by-its-norm-of-the-column

评论： M 2022-4-9

采纳的回答： Torsten

If there is array with size (2*3*128) and I want to divid each column over its norm.

How to do that?

For example this is part of the matrix

val(:,:,1) =

-0.0401 -0.2077 0.4750

-0.3867 -1.7742 3.3940

val(:,:,2) =

-0.0259 -0.1569 0.3964

-0.2504 -1.3830 3.1329

I want each column such as -0.0401 to divid it over its norm and same for other column

-0.3867

2nd column -0.2077 divid it over its norm

-1.7742

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M 2022-4-9

@Image Analyst as @Torsten said the second element of the column listed in the next line

Image Analyst 2022-4-9

在 MATLAB Online 中打开

Arrays are indexed like (row, column, slice). So by column, you don't mean dimension 2

val = 5*rand(2,3,128);
col2 = val(:, 2, :); % Get the second column -- all values of dimension 2
whos col2
  Name      Size               Bytes  Class     Attributes

  col2      2x1x128             2048  double              
col2 = squeeze(col2) % Turn from 3-D array into 2-D matrix
col2 = 2×128
    1.6494    1.7078    0.5240    4.1775    4.6723    0.8532    1.7875    2.8801    0.8354    4.9773    2.5038    4.2715    2.1833    2.8106    2.6810    0.2129    3.3235    1.1497    2.5837    4.5390    3.5507    3.4277    1.2060    3.0198    3.1786    1.5361    1.3881    4.4988    3.9208    2.5136
    2.8813    2.0693    3.8127    1.7947    3.8008    4.7853    4.6437    3.5783    3.8805    4.8341    2.9445    0.0719    0.9767    1.8386    0.4462    2.3776    0.3446    2.2689    0.9295    1.4432    4.7759    4.8002    0.3142    1.1288    1.1407    2.2899    1.8586    0.8476    2.4115    2.9267
whos col2
  Name      Size             Bytes  Class     Attributes

  col2      2x128             2048  double              

but you mean like a vertical vector perpendicular to the slices going down through the 128 slices. Like one vector of 128 would be val(1,1,:), and another vector of 128 would be val(1,2,:), and so on. Is that right?

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Answer 1

Torsten 2022-4-9

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https://ww2.mathworks.cn/matlabcentral/answers/1692570-divide-each-column-of-an-array-by-its-norm-of-the-column#answer_938705

编辑：Torsten 2022-4-9

在 MATLAB Online 中打开

A = A./vecnorm(A,2)

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M 2022-4-9

@Torsten Thanks

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Answer 2

Image Analyst 2022-4-9

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1692570-divide-each-column-of-an-array-by-its-norm-of-the-column#answer_938710

在 MATLAB Online 中打开

Is this possibly what you're trying to describe?

val = 5 * rand(2, 3, 128); % Sample data.
[rows, columns, slices] = size(val);
% Get norms
theNorms = zeros(rows, columns);
for col = 1 : columns
    for row = 1 : rows
        v = squeeze(val(row, col, :));
        theNorms(row, col) = norm(v);
    end
end
% Divide each value by the norm for that (row, column) location.
output = zeros(rows, columns, slices);
for slice = 1 : slices
    for col = 1 : columns
        for row = 1 : rows
            thisNorm = theNorms(row, col);
            output(row, col, slice) = val(row, col, slice) / thisNorm;
        end
    end
end