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  • Subject: [mg21427] Re: CALCULATION TIME
  • From: Jens-Peer Kuska <kuska at>
  • Date: Fri, 7 Jan 2000 00:20:38 -0500 (EST)
  • Organization: Universitaet Leipzig
  • References: <851ek8$>
  • Sender: owner-wri-mathgroup at


whats wrong ? The Do[]-Loops ? You should look into your expression
to express the operations with highlevel commands like Dot[],
ListConvolve[], Fold[] ...

I use rather seldom Do[]'s and For[]'s and I have never missed it.
operators like Map[], Apply[] are typical faster.

You supply not the information to give you more hints.


Blimbaum Jerry DLPC wrote:
>         I have some code performing (roughly) the following Do Loops:
>         Do[.........
>                      Do[x[[m,n+1]] = x[[m,n]] + B*       y[[n+m-1]]*e[[n]]
> ----------------------------------------------,
> eps+Sum[y[[n-q]]^2,{q,0,M-1}]
>                   {m,M}        ],
>                 {n,M,Length[y]}]
>         where y, e are lists (y is data that contains about 30000 elements),
> etc.     Running a data set takes about 10.5 secs.  I wanted to shorten the
> time but couldnt figure out how to write it either in Nest or Compile form
> so I went thru it piece meal to see if I could find a culprit and from this
> I noticed if I replace the Sum term in the denominator by a number, lets say
> 1, and then perform the calculations it only takes about 2.5 seconds!   I
> did a sample Sum[expr^2] with a similar Do loop separately and it takes no
> time at all.
>         What is wrong?
>         thanks.   Jerry Blimbaum    NSWC   Panama City, Fl

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