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MathGroup Archive 2004

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Re: matrix operations

  • To: mathgroup at smc.vnet.net
  • Subject: [mg46353] Re: matrix operations
  • From: "Steve Luttrell" <steve1 at _removemefirst_luttrell.org.uk>
  • Date: Mon, 16 Feb 2004 08:59:53 -0500 (EST)
  • References: <c0mohe$65t$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Here is an example of what you want to do:

a=Array[x,{10,3}]

Map[(#1[[2]]-#1[[1]])&,Partition[a,2,1]]

Steve Luttrell

"paolo tarpanelli" <tarpanelli at libero.it> wrote in message
news:c0mohe$65t$1 at smc.vnet.net...
> 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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