Re: Matrix operation

*To*: mathgroup at smc.vnet.net*Subject*: [mg125765] Re: Matrix operation*From*: Bob Hanlon <hanlonr357 at gmail.com>*Date*: Sun, 1 Apr 2012 03:38:44 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <201203310845.DAA13058@smc.vnet.net>

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}}; s2 = -s1; s2 = ReplacePart[s2, 4 -> -s1[[4]] - 4 s1[[3]]]; Bob Hanlon On Sat, Mar 31, 2012 at 4:45 AM, Andrey Demidov <andrey.demidov at gmail.com> wrote: > Hi, > > 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 ? >