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Re: Matrix Manipulation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg16427] Re: Matrix Manipulation
  • From: Hartmut Wolf <hw at gsmail01.darmstadt.dsh.de>
  • Date: Sat, 13 Mar 1999 02:21:42 -0500
  • Organization: debis Systemhaus
  • References: <7c5bl0$7rt@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Dear Andreas

Andreas Paul Friedrich Bernhard schrieb:
> 
> I am trying to modify the elements of a submatrix in a matrix, without
> having to replace each element explicitly
> 
> for example:
> mm   = { {1,2,3}, {4,5,6}, {7,8,9} }
> msub      = { {21,22}, {23,24} }
> I now wish to add the sub matrix: to positions (1,1),(1,3),(3,1),(3,3)
> 

  p={{1,1},{1,3},{3,1},{3,3}};

  MapAt[#+msub&, mm, p]

gives -->

  {{ {{22,23},{24,25}}, 2, {{24,25},{26,27}} },
   {        4,          5,        6          },
   { {{28,29},{30,31}}, 8, {{30,31},{32,33}} }}

(spaces adjusted by hand to mimik TableForm)

---Hartmut


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