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How do I create this in MATLAB?
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James Tursa
James Tursa 2019-8-22
What have you done so far? What specific problems are you having with your code? Do you know how to write a for-loop, or use the sum( ) function, or use the diff( ) function, or use the .* operator?
John Allen
John Allen 2019-8-22
Yes, I know all of those, just never did it like this, so totally confused how to structure this one.

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James Tursa
James Tursa 2019-8-23
编辑：James Tursa 2019-8-23

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Take the denominator for instance. Literally written out, this would be
denominator = 0;
for k=1:K
denominator = denominator + B(k,j)^2;
end
Or, assuming the first dimension of B is K, then you could use the sum( ) function:
denominator = sum(B(:,j).^2);
You can construct similar code for the numerator.
Probably best if you code everything up using for-loops just to get something running that works. Then you can simplify things with the sum( ) and diff( ) functions. It is possible to do the entire operation to construct ds without loops.

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John Allen
John Allen 2019-8-23
In my application, it is NMF based operation, so the matrix is K x T and I have J components, let's say 20 of them, and then after I apply NMF, I will get B = K x J and G = J x T.
This summation happens after I get B. So, wouldn't I need a nested 2d loop to go over both K and J ?
I understand your code, but I am trying to understand this in my head.
James Tursa
James Tursa 2019-8-23
编辑：James Tursa 2019-8-23
"So, wouldn't I need a nested 2d loop to go over both K and J ?"
Yes. The code I had written above was only for the denominator part of the j'th element of ds.
I would still suggest you write out the looping code first to get some correct code running. Then you can worry about simplifying it using sum( ) and diff( ) etc.
John Allen
John Allen 2019-8-23
OK, thank you very much, I think I get it now, I marked answer as accepted.
Thanks again! :)
James Tursa
James Tursa 2019-8-23
If you have trouble, don't hesitate to post your current code and the problems you are having and we can still help you.

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