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MathGroup Archive 2004

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Re: matrix operations

  • To: mathgroup at smc.vnet.net
  • Subject: [mg46344] Re: matrix operations
  • From: bobhanlon at aol.com (Bob Hanlon)
  • Date: Mon, 16 Feb 2004 08:59:46 -0500 (EST)
  • References: <c0mohe$65t$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

a = Array[x, {3,4}]

{{x[1, 1], x[1, 2], x[1, 3], x[1, 4]}, 
  {x[2, 1], x[2, 2], x[2, 3], x[2, 4]}, 
  {x[3, 1], x[3, 2], x[3, 3], x[3, 4]}}

r=Module[{at=Transpose[a]},
    Transpose[Rest[#-RotateRight[#]]& /@ at]]

{{x[2, 1] - x[1, 1], x[2, 2] - x[1, 2], 
   x[2, 3] - x[1, 3], x[2, 4] - x[1, 4]}, 
  {x[3, 1] - x[2, 1], x[3, 2] - x[2, 2], 
   x[3, 3] - x[2, 3], x[3, 4] - x[2, 4]}}

r == Table[a[[m+1,n]]-a[[m,n]],
    {m,Length[a]-1},{n,Length[First[a]]}]

True


Bob Hanlon

In article <c0mohe$65t$1 at smc.vnet.net>, "paolo tarpanelli"
<tarpanelli at libero.it> wrote:

<< 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}]]


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