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addressing matrix elements

  • To: mathgroup at smc.vnet.net
  • Subject: [mg3566] addressing matrix elements
  • From: drc at emi.net (David Cabana)
  • Date: Mon, 25 Mar 1996 21:33:49 -0500
  • Organization: CyberGate, Inc.
  • Sender: owner-wri-mathgroup at wolfram.com

The Mma language sometimes drives me crazy.  If I don't practice it
regularly, I seem to forget everything.  Here's what I want to do, but
can't.

Say M is a matrix of integers.  I want to func[M, k] to return a matrix
same dimensions as M, each entry consisting of the corresponding entry of
M taken modulo k.  For instance, func[{{22,33}, {44,55}}, 10] should
return {{2,3}, {4,5}}.  I would like this to work for arbitrary
rectangular integer matrices, but am not having much luck.  It seems like
this should be easy,  but I'm stumped.  

More generally, I would like to be able to apply a function f to each
element in a matrix of arbitrary size and dimensions, without worrying
about the particulars of the matrix representation via lists.  I want
func[M, g] to return a matrix of the same size and shape as M, with
elements formed by applying g to corresponding elements of M.  Is there
nice way to do this?  Seems like some combination  of Map, Apply, Thread,
SetAttributes Listable, Outer, etc. could do the job, but I am lost in the
morass of possibilites.   Any help would be appreciated.

Thanks,

-- 
David Cabana    drc at gate.net 

"Ask the American public if they want an FBI Wiretap and they'll say 'no.'  If you ask them do they want a feature on their phone that helps the FBI find their missing child they'll say, 'Yes.'"
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Telecommunications & Finance) hearing on the Digital Telephony bill, 09/13/94). 

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  - Edmund Burke

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