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}}