If he has J6.01, which is using the old floating-point unit, a factor of 2x-5x could be had from the tightest coding using SSE instructions; and then if MatLab uses multiple cores effectively, a 10x performance diff is not out of the question.
Henry Rich > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Roger Hui > Sent: Thursday, November 08, 2007 5:51 PM > To: Programming forum > Subject: Re: [Jprogramming] Re: speed of matrix*vector operation > > > The j version runs about a factor of 10 slower than the > > matlab version, but at least my earlier timing dropped from > > 2.5 minutes to about 5 seconds. > > Yes, but have you included the time to generate the > random numbers in your MatLab benchmark? > Because you are including it in your J benchmark. > The following illustrates the difference: > > 1000 * 1000 (6!:2) '(?256$0)+/ . *?256 312$0' > 6.22474 > > x=: 256 [EMAIL PROTECTED] 0 > y=: 256 312 [EMAIL PROTECTED] 0 > 1000 * 1000 (6!:2) 'x +/ .* y' > 0.56505 > > For something as common and as important as matrix multiply > I imagine that MatLab would have had the best efforts of > their hotshot implementers. Likewise in J. I am skeptical > that the MatLab hotshot implementers would be better than > the J hotshot implementers by a factor of 10. > > p.s. Have you tried the Hilbert matrix experiment? > > > > > ----- Original Message ----- > From: [EMAIL PROTECTED] > Date: Thursday, November 8, 2007 14:35 > Subject: [Jprogramming] Re: speed of matrix*vector operation > To: [email protected] > > > Sorry, I did not properly explain my problem. > > > > Anyhow, by using: > > > > 1000 (6!:2) '(?256$0)+/ . *?256 312$0' > > 0.0052153 > > > > which is about 5.2 seconds to do 1000 iterations of the > > matrix times vector multiply. > > > > BIG reduction in time obtained by using ordinary numbers and > > NOT using extended precision numbers. > > > > Also, not writing a program is cool. > > > > The j version runs about a factor of 10 slower than the > > matlab version, but at least my earlier timing dropped from > > 2.5 minutes to about 5 seconds. > > > > thanks a lot for the ideas. > > > ---------------------------------------------------------------------- > For information about J forums see > http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
