Re: Manipulating a matrix
- To: mathgroup at smc.vnet.net
- Subject: [mg59241] Re: [mg59212] Manipulating a matrix
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Wed, 3 Aug 2005 01:19:46 -0400 (EDT)
- Reply-to: hanlonr at cox.net
- Sender: owner-wri-mathgroup at wolfram.com
mat=Array[a,{4,4}]
{{a[1, 1], a[1, 2], a[1, 3], a[1, 4]}, {a[2, 1], a[2, 2], a[2, 3], a[2, 4]},
{a[3, 1], a[3, 2], a[3, 3], a[3, 4]}, {a[4, 1], a[4, 2], a[4, 3], a[4, 4]}}
To drop the first row and first column:
mat2=Rest[Rest/@mat]
{{a[2, 2], a[2, 3], a[2, 4]}, {a[3, 2], a[3, 3], a[3, 4]},
{a[4, 2], a[4, 3], a[4, 4]}}
To drop the third row and second column:
Drop[Drop[#,{2}]&/@mat,{3}]
{{a[1, 1], a[1, 3], a[1, 4]}, {a[2, 1], a[2, 3], a[2, 4]},
{a[4, 1], a[4, 3], a[4, 4]}}
Also look at the standard add-on package
LinearAlgebra`MatrixManipulation`
Needs["LinearAlgebra`MatrixManipulation`"];
TakeMatrix[mat,{2,2},{4,4}]==
SubMatrix[mat,{2,2},{3,3}]==
mat2
True
Bob Hanlon
>
> From: "Ramier" <wissam2 at online.fr>
To: mathgroup at smc.vnet.net
> Date: 2005/08/02 Tue AM 12:42:32 EDT
> Subject: [mg59241] [mg59212] Manipulating a matrix
>
> Hello everyone,
>
> I think that my question is rather simple and maybe I ought to go
> deeper into Mathematica book:
> I have a n x n matrix and I'd like to remove the first line and the
> first column in order to get the (n-1)x(n-1) matrix with the entries
> remaining. Is there a simple way to do that ?
>
> Perhaps my question is really simple or idiot but I've never used
> Mathematica before.
>
> Thanks a lot,
>
> Wissam
>
>