Re: Why Does Repeated Dot Product Take So Long?
- To: mathgroup at smc.vnet.net
- Subject: [mg67946] Re: Why Does Repeated Dot Product Take So Long?
- From: "Jens-Peer Kuska" <kuska at informatik.uni-leipzig.de>
- Date: Tue, 18 Jul 2006 05:50:30 -0400 (EDT)
- Organization: Uni Leipzig
- References: <e9frif$2lp$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Hi, my Dual Pentium say With[{n = 2000000}, x = Table[Random[], {n}, {3}]; y = Table[Random[], {n}, {3}]; Timing[ Table[Dot[x[[i]], y[[i]]], {i, n}] ] ] // First 2.172 Second and Timing[MapThread[Dot, {x, y}]] Dot @@@ Transpose[{x, y}] are mutch slower ... May be you should blame the PowerPC processor ... Regards Jens "Gregory Lypny" <gregory.lypny at videotron.ca> schrieb im Newsbeitrag news:e9frif$2lp$1 at smc.vnet.net... | 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 |