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FW: RE: matrix operations
*To*: mathgroup at smc.vnet.net
*Subject*: [mg46383] FW: [mg46343] RE: [mg46329] matrix operations
*From*: "E. Martin-Serrano \(Houston\)" <eMartinSerrano at houston.rr.com>
*Date*: Mon, 16 Feb 2004 23:42:16 -0500 (EST)
*Sender*: owner-wri-mathgroup at wolfram.com
Hi,
I have put this David's response in a notebook called "The wonders of
functional programming (by David Park).nb", mainly, because of the use he
does of "%". Notice the "spaces" and "parenthesis" in the file's name, and
its length as a string.
Spaces and length in Mathematica file names is something that has always
worried me:
My question is: while this file name is instructive, for the purpose of
maintaining a library and documentation. Which are the implications from the
side of the capability of Mathematica in handling package names, and such
strings of characters as symbols?
E. Martin-Serrano
-----Original Message-----
From: David Park [mailto:djmp at earthlink.net]
To: mathgroup at smc.vnet.net
Subject: [mg46383] [mg46343] RE: [mg46329] matrix operations
Paolo,
The wonders of functional programming! Here's an example.
mat = Array[x, {4, 4}]
Partition[mat, 2, 1]
(answer = #2 - #1 & @@@ %) // MatrixForm
@@@ is the Apply function, mapped onto the first level of mat. #2 - #1& is a
pure function that subtracts the second argument from the first argument.
David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/
-----Original Message-----
From: paolo tarpanelli [mailto:tarpanelli at libero.it]
To: mathgroup at smc.vnet.net
Subject: [mg46383] [mg46343] [mg46329] matrix operations
If I have a matrix
a={x[[1,1]],x[[1,2]],...,x[[1,n]]}
{x[[2,1]],x[[2,2]],...,x[[2,n]]}
.
.
.
{x[[m,1]],x[[m,2]],...,x[[m,n]]}
how can I compute the difference between any element and the previous for
each column :
aa={x[[2,1]]-x[[1,1]], x[[2,2]]-x[[1,2]],...,x[[2,n]]-x[[1,n]]}
{x[[3,1]]-x[[2,1]], x[[3,2]]-x[[2,2]],...,x[[3,n]]-x[[2,n]]}
.
.
.
{x[[m,1]]-x[[m-1,1]],x[[m,2]]-x[[m-1,2]],...,x[[m,n]]-x[[m-1,n]]}
----------------------------------------------------------------------------
--------------------------
I built this code but it does not work
r=Array[0,{m,n}]
For[j=1,j=n,j++
r[[i,j]]=Table[a[[i+1,j]]-a[[i,j]],{i,1,m-1,1}]]
thanks
Paolo
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