MATLAB code that can replace the inbuilt function 'norm'

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Yue Han Seow 2019-3-15

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https://ww2.mathworks.cn/matlabcentral/answers/450188-matlab-code-that-can-replace-the-inbuilt-function-norm

评论： Yue Han Seow 2019-3-15

Hello, I need to substitute the inbuilt function 'norm' with other matlab code that execute the same function. This is because the function 'norm' is not permitted to be translated using the MATLAB HDL Coder function.

Thank you in advance for the help!

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John D'Errico 2019-3-15

As importantly, what is win? Is win a vector? Is win a matrix?

Yue Han Seow 2019-3-15

win is a window

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John D'Errico 2019-3-15

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https://ww2.mathworks.cn/matlabcentral/answers/450188-matlab-code-that-can-replace-the-inbuilt-function-norm#answer_365518

编辑：John D'Errico 2019-3-15

在 MATLAB Online 中打开

I suppose I can write a simple 1-norm code, that will work for a vector OR matrix.

Thus, the 1-norm of a vector is the sum of absolute values of the vector. So, if X is a vector, then norm(X,1) == sum(abs(X)).

If X is a matrix? Then the 1-norm is the maximum sum of all columns of the matrix. We can see how this works:

X = rand(3,3)
X =
      0.72105      0.21868     0.063591
       0.5225       0.1058      0.40458
       0.9937       0.1097      0.44837
>> norm(X)
ans =
       1.4581
>> max(sum(abs(X),1))
ans =
       2.2372
>> norm(X,1)
ans =
       2.2372

So now we can write a code that will work for any vector or matrix, computing the 1-norm.

function res = norm1(X)
if isvector(X)
   res = sum(abs(X));
else
   res = max(sum(abs(X),1));
end

This code does not replace norm, in the sense that it is far simpler. It does not compute a 2-norm, or any other norm. It does not work for 3-d matrices, but then, neither does norm work there.