trying to write matlab code for Frobenius norm of an mxn matrix

Question

shelly 2013-2-23

0
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https://ww2.mathworks.cn/matlabcentral/answers/64673-trying-to-write-matlab-code-for-frobenius-norm-of-an-mxn-matrix

回答： Rolando Molina 2018-4-13

Hello, hoping someone can guide me, i asked my question on another forum, but realised this place could have better help,....with matlab, I have provided the link below, cause I cannot write the mathematical formula on here,

http://www.physicsforums.com/showthread.php?t=673897

any help greatly appreciated.

the code i have written so far is

function w = frobeniusnorm(a,m,n) for i =1:m sm = 0 for j =1:n sm = sm+A(i,j)*a^2(i,j); end

which does not work

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Muthu Annamalai 2013-2-23

在 MATLAB Online 中打开

The problem with your code, Shelly, seems to be

function w = frobeniusnorm(a,m,n)
  for i =1:m
    sm = 0
    for j =1:n
      sm = sm+A(i,j)*a^2(i,j);
    end
  end
end

you have sm = 0, reinitialized every time. You need to move it out of the first for-loop.

A better solution without using the built-in norm() function is to write out sums,

sm = sqrt( sum(sum(A.^2)) )

I would strongly recommend you read the MATLAB tutorial on matrix indexing http://www.mathworks.com/help/matlab/math/matrix-indexing.html and use what is called 'vectorized code'

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