Re: addressing matrix elements
- To: mathgroup at smc.vnet.net
- Subject: [mg3584] Re: addressing matrix elements
- From: Jorma.Virtamo at vtt.fi (Jorma Virtamo)
- Date: Wed, 27 Mar 1996 03:26:04 -0500
- Sender: owner-wri-mathgroup at wolfram.com
drc at emi.net (David Cabana) wrote:
>
> 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,
>
In general you have to make g listable:
SetAttributes[g,Listable]
Then,
In[] := g[{{22,33}, {44,55}}]
Out[] = {{g[22], g[33]}, {g[44], g[55]}}
The Mod-function is listable, so it works directly:
In[] := Mod[{{22,33}, {44,55}},10]
Out[] = {{2, 3}, {4, 5}}
-- Jorma Virtamo
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jorma Virtamo VTT Information Technology
phone: +358 0 456 5612 Telecommunications
fax: +358 0 455 0115 P.O. Box 1202
email: jorma.virtamo at vtt.fi FIN-02044 VTT
web: http://www.vtt.fi/tte/ Finland
==== [MESSAGE SEPARATOR] ====