Re: Matrix operation
- To: mathgroup at smc.vnet.net
- Subject: [mg125759] Re: Matrix operation
- From: Bill Rowe <readnews at sbcglobal.net>
- Date: Sun, 1 Apr 2012 03:36:09 -0400 (EDT)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
On 3/31/12 at 3:45 AM, andrey.demidov at gmail.com (Andrey Demidov)
wrote:
>I have a matrix:
>>>s1 = {{0, 4, 3, 6, 1, 0, 0, 30}, {0, 6, 16, 8, 0, 1, 0, 256}, {0,
>>>4, 1,
>10, 0, 0, 1, 9}, {1, -2, -4, -3, 0, 0, 0, 0}}
>>>MatrixForm[s1]
>Now, I need to get another matrix (s2) where:
>- s2[i, j] = s1[i, j] where i <> 4
>- s2[i, j] = s1[i, j] + 4 * s1[i - 1, j] where i == 4
>What is the best way to get s2 ?
Best depends on what criteria you use to define best. Meanwhile,
here is one way to do what you want
In[3]:= Join[Most@s1, {Transpose[s1[[-2 ;;]]].{1, 4}}]
Out[3]= {{0, 4, 3, 6, 1, 0, 0, 30}, {0, 6, 16, 8, 0, 1, 0, 256},
{0, 4, 1, 10, 0, 0, 1, 9}, {4, -4, -15, -2, 0, 0, 1, 9}}