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Re: surprising timings for multiplication of diagonalmatrix and full matrix

  • To: mathgroup at smc.vnet.net
  • Subject: [mg124964] Re: surprising timings for multiplication of diagonalmatrix and full matrix
  • From: danl at wolfram.com
  • Date: Tue, 14 Feb 2012 06:41:06 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <jhaiip$56k$1@smc.vnet.net>

I suspect Dot packs first when it can. So when you are under the threshold of packed array size (250, in this case), your various functions are working with unpacked inputs. The ones that "know" to pack first come out ahead.

Fastest would  (well, should) be to use Times:

w = Timing[Do[fd = bsd*asd, {nj}]][[1]] 


Daniel Lichtblau
Wolfram Research



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