How to find magnitude of an array of 17 vectors

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Sarah Hicks 2018-9-3

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回答： Steven Lord 2019-6-24

采纳的回答： madhan ravi

I have imported a txt file and need to find the magnitude of the 17 vectors on the file. Thanks.

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madhan ravi 2018-9-3

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编辑：madhan ravi 2018-9-3

在 MATLAB Online 中打开

Use :

norm(x) %x - is a vector, norm syntax calculates the magnitude of the vector

*AN EXAMPLE: *

X= rand(10,10)
size(X)
for i = 1:length(X)
      MAG(i,:) = norm(X(i,:)); %calculates the magnitude of 10 vectors separately in each iteration
end
MAG
size(MAG)

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Image Analyst 2018-9-3

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Length() gives the longest dimension. I don't think it's a good idea to use it on a matrix. I use it only on vectors. For some reason the lamelli.txt file got removed from the post. If it's only 2 or 3 columns, it should be okay but if it has more than 17 columns, there will be a problem. Plus you shouldn't use i as a loop index, and you don't need a second dimension for MAG. To be more robust, here is how I'd do it:

data = load('lamelli.txt')
[rows, columns] = size(data)
magnitudes = zeros(rows, 1); % Preallocate
for k = 1: rows
  magnitudes(k) = norm(data(k,:));
end
magnitudes      % Print to command window.
whos magnitudes % Print info to command window.

madhan ravi 2018-9-3

Thank you @sir Image Analyst much appreciated.

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Steven Lord 2019-6-24

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If you're using release R2017b or later, use the vecnorm function to compute the norm of vectors stored in an array.

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Joshua Daniels 2019-6-24

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编辑：Joshua Daniels 2019-6-24

sqrt(sum(data.^2,dim)) where dim is the dimention that your vectors are written in. ie a 5x3 vertical list of horizontal vectors would use dim=2 since each vector is in the horizontal dimention.