Why Does Repeated Dot Product Take So Long?
- To: mathgroup at smc.vnet.net
- Subject: [mg67938] Why Does Repeated Dot Product Take So Long?
- From: Gregory Lypny <gregory.lypny at videotron.ca>
- Date: Mon, 17 Jul 2006 06:51:55 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Hello Everyone,
x and y are both 2000 x 3 matrices. I wanted to created a 2000 x 1
vector with each element equal to the dot product of the
corresponding rows of x and y. So I tried this:
Table[x[[i]].y[[i]], {i, 1, 2000}]
It took more than two and a half minutes on my iBook G4. Is that
normal? I've done seemingly more demanding computations in Do loops
and Tables that are completed in a split second. Am I doing
something wrong with this one?
Regards,
Gregory
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