Random dot product tricks

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Jesse
Jesse 2013-9-27
评论： Jesse 2013-9-29
Greetings again,
I have two arrays:
x = [1.3, 5.6, 7.8, -6.5, 0.3]
y = [134.2, 8786.98, -22.4, 4553518.6, 0.0019]
Now, I know how to do the dot product
a=dot(x,y)
and the reverse (i.e, the first dot product has the summation from 1 to 5, but the reverse is 5 to 1),
so
xback = fliplr(x);
yback = fliplr(y);
b=dot(x,y)
but what about largest-to-smallest order dot produc? Is there anyway to organize that in MATLAB from the original arrays?
I didn't know if this was with the sort command.
Thanks!

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采纳的回答

Walter Roberson
Walter Roberson 2013-9-27
编辑：Walter Roberson 2013-9-27
xy = x.*y;
dotxy = sum(sort(xy(xy>0), 'descend')) + sum(sort(xy(xy<0)));
  1 个评论
Jesse
Jesse 2013-9-29
Yes - that's what I was looking for. Very tight too!
Thanks Walter!

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更多回答（1 个）

Azzi Abdelmalek
Azzi Abdelmalek 2013-9-27
编辑：Azzi Abdelmalek 2013-9-27
If you sort a or b or both the result will be different.
Maybe you want to do other thing. Clarify what you want to achieve
% dot(a,b) is the same then sum(a.*b)
  3 个评论
显示 1更早的评论
Azzi Abdelmalek
Azzi Abdelmalek 2013-9-27
No this is not clear, illustrate with a numeric example
Jan
Jan 2013-9-27
编辑：Jan 2013-9-27
What is your purpose of creating the partial sums at first? Do you want to increase the accuracy of the result? Then better use FEX: XSum: XSum(a .* b).

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