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

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M on 9 Apr 2022
Commented: M on 9 Apr 2022
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
Image Analyst on 9 Apr 2022
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?

Torsten on 9 Apr 2022
Edited: Torsten on 9 Apr 2022
A = A./vecnorm(A,2)
M on 9 Apr 2022
@Torsten Thanks

Image Analyst on 9 Apr 2022
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
M on 9 Apr 2022
@Image Analyst , Actually this is just what i am trying to do : A = A./vecnorm(A,2)
Thanks