Re: row,column question

*To*: mathgroup at smc.vnet.net*Subject*: [mg73371] Re: row,column question*From*: Paul Abbott <paul at physics.uwa.edu.au>*Date*: Wed, 14 Feb 2007 05:21:30 -0500 (EST)*Organization*: The University of Western Australia*References*: <eqs94u$ihh$1@smc.vnet.net>

In article <eqs94u$ihh$1 at smc.vnet.net>, John Biddiscombe <biddisco at cscs.ch> wrote: > If I have a 4x4 matrix and I postmultiply by {{1,0,0,bx}} I actually get > something like col1 + bx*col4 > > Is there any way of telling Mathematica to show the result in a symbolic form > using (for example, rows and columns) in this case. If mat is an m x n matrix, say mat = Table[a[i, j], {i, 3}, {j, 4}]; and b is an n-vector, say b = {1,0,0,bx}; and c is an m-vector, say c = {2,0,cx}; then, after defining cols[mat_] := Array[col, Last@Dimensions[mat]] rows[mat_] := Array[row, First@Dimensions[mat]] which, essentially, replaces the matrix, mat, by a symbolic vector of columns or rows, one sees that cols[mat] . b col[1] + bx col[4] or c . rows[mat] 2 row[1] + cx row[3] does what you want. You can recover the actual matrix entries as % /. {row[i_] :> mat[[i, All]], col[j_] :> mat[[All, j]]} Cheers, Paul _______________________________________________________________________ Paul Abbott Phone: 61 8 6488 2734 School of Physics, M013 Fax: +61 8 6488 1014 The University of Western Australia (CRICOS Provider No 00126G) AUSTRALIA http://physics.uwa.edu.au/~paul