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Re: Why Does Repeated Dot Product Take So Long?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg67950] Re: [mg67938] Why Does Repeated Dot Product Take So Long?
  • From: Sseziwa Mukasa <mukasa at jeol.com>
  • Date: Tue, 18 Jul 2006 05:50:35 -0400 (EDT)
  • References: <200607171051.GAA02347@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

What is in x and y?

Using matrices of machine precision real numbers it take about 3ms on  
a dual 2.5GHz G5 for me.

Regards,

Ssezi

On Jul 17, 2006, at 6:51 AM, Gregory Lypny wrote:

> 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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