How to use the dot product within a loop to multiply a series of rows?!

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Joshua Otter
Joshua Otter 2014-3-24
回答： James Tursa 2014-3-25
I currently have two matrices.
- V = (1*3) matrix
- coordNORMALS = (18766*3) matrix.
I would like to take the dot product of the two such that:
- C = dot ( V, coordNORMALS)
I understand that to take the dot product the size of the two matrices must be equal, however I would like to find C for each row, i.e get 18766 values of C
C = dot ( V, coordNORMALS (1 , : )) all the way to C = dot ( V, coordNORMALS ( end , : ))
I have tried to use a loop in the following format but end up in an infinite loop:
for i=1:length(coordNORMALS)
C(i) = dot(V,coordNORMALS(i,:))
end
end
If anyone knows how to help, please reply
Many Thanks Josh

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采纳的回答

Gareth Thomas
Gareth Thomas 2014-3-24
V = rand(1,3)
C = rand(13,3)
dot(V,C(1,:))
dot(V,C(2,:))
for i = 1:length(C)
d(i) = dot(V,C(i,:));
end
Does this not work?
  1 个评论
Joshua Otter
Joshua Otter 2014-3-24
It works fine, just me being an idiot. I had the answers coming up in the command window which took ages to load so I thought I was stuck in an infinite loop. Thanks Gareth.

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更多回答（1 个）

James Tursa
James Tursa 2014-3-25
A direct matrix multiply is likely to be faster than using dot. E.g., assuming the variables are real:
C = coordNORMALS * V.';

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