MathGroup Archive 2004

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Many thanks, again...

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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