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MathGroup Archive 2004

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Many thanks, again...

  • To: mathgroup at
  • Subject: [mg50340] Many thanks, again...
  • From: "1.156" <rob at>
  • Date: Sat, 28 Aug 2004 04:37:52 -0400 (EDT)
  • References: <cgkg6v$g97$>
  • Sender: owner-wri-mathgroup at

As usual the folks on this group delivered varied and very instructive 
ways to do the job.  Your suggestions
are good targets for me to attempt to understand -- and I don't yet, 

Thanks very much for giving your time to help. 
Regards, Rob

1.156 wrote:

>I realize that many times some form of Mathematica built in array function will
>do the needed job.  Here I have a matrix containing individual data
>traces in rows y[[i]]. I want to make matrix containing the corresponding
>derivative signals in rows yd[[i]].  I get this done using the following
>For loop. Matrix yd has been initialized (it wouldn't work with out it).
>For[i = 1, i < n, i++, yd[[i]] = Drop[RotateLeft[y[[i]]] - y[[i]], -1]];
>I tried the obvious (to me):
>yd = Drop[RotateLeft[y] -y, -1];
>But I get garbage.  It seems the whole matrix has been flattened to a
>single list and the whole list is rotated --instead of doing it row
>by row as I need.
>Wizzards all: is there some slick way to do this without the For loop?
>If so, it's probably faster and sure would look better in the code.
>Suggestions appreciated as usual.

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