Re: Matrix Inverse Issue

*To*: mathgroup at smc.vnet.net*Subject*: [mg80628] Re: [mg80556] Matrix Inverse Issue*From*: Sseziwa Mukasa <mukasa at jeol.com>*Date*: Sun, 26 Aug 2007 23:25:35 -0400 (EDT)*References*: <200708260700.DAA03587@smc.vnet.net>

On Aug 26, 2007, at 3:00 AM, Brian Gladman wrote: > I am having a problem with the matrix inverse for the following > matrix in > Mathematica 6: > > A = Table[If[j == i, 1 - i/10, If[j == i + 1, i/10, 0]], {i, 9}, > {j, 9}] > > {{9/10, 1/10, 0, 0, 0, 0, 0, 0, 0}, {0, 4/5, 1/5, 0, 0, 0, 0, 0, > 0}, {0, 0, 7/10, 3/10, 0, 0, 0, 0, 0}, {0, 0, 0, 3/5, 2/5, 0, 0, 0, > 0}, {0, 0, 0, 0, 1/2, 1/2, 0, 0, 0}, {0, 0, 0, 0, 0, 2/5, 3/5, 0, > 0}, {0, 0, 0, 0, 0, 0, 3/10, 7/10, 0}, {0, 0, 0, 0, 0, 0, 0, 1/5, 4/ > 5}, {0, 0, 0, 0, 0, 0, 0, 0, 1/10}} > > A Inverse[A] > > {{1, -1/72, 0, 0, 0, 0, 0, 0, 0}, {0, 1, -1/14, 0, 0, 0, 0, 0, 0}, {0, > 0, 1, -3/14, 0, 0, 0, 0, 0}, {0, 0, 0, 1, -8/15, 0, 0, 0, 0}, {0, > 0, 0, 0, 1, -5/4, 0, 0, 0}, {0, 0, 0, 0, 0, 1, -3, 0, 0}, {0, 0, 0, > 0, 0, 0, 1, -49/6, 0}, {0, 0, 0, 0, 0, 0, 0, 1, -32}, {0, 0, 0, 0, > 0, 0, 0, 0, 1}} > > I expected the identity matrix here but I get extra terms. > > Am I doing something wrong? Use Dot for matrix multiplication eg: A.Inverse[A] Regards, Ssezi

**References**:**Matrix Inverse Issue***From:*"Brian Gladman" <brg@nowhere.org>