Solve

*To*: mathgroup at smc.vnet.net*Subject*: [mg2060] Solve*From*: FERRUCCIO Renzoni <renzoni at fexphds04.tu-graz.ac.at>*Date*: Sat, 23 Sep 1995 20:33:50 -0400

Dear wizards, I have to solve the sistem a.x = v where v= {1,0,0,0,0,0,0,0,0} and a is a 9x9 symbolic matrix. If I use LinearSolve[a,v] I get an enormous expession, so I think should be possible invert the system "step by step", for exemple using: x = {x1,x2,x3,x4,x5,x6,x7,x8,x9}; Do[ eqn[i] = { a[[i]].x == v[[i]]} ,{i,1,9}] a = Solve[ eqn[1],x1][[1]]; b = Solve[ Simplify[eqn[2] /.a],x2][[1]]; c = Solve[ Simplify[eqn[3] /.a/.b],x3][[1]]; d = Solve[ eqn[4] /.a/.b/.c,x4][[1]]; e = Solve[ eqn[5] /.a/.b/.c/.d,x5][[1]]; f = Solve[ eqn[6] /.a/.b/.c/.d/.e,x6][[1]]; l = Solve[ eqn[7] /.a/.b/.c/.d/.e/.f,x7][[1]]; m = Solve[ eqn[8] /.a/.b/.c/.d/.e/.f/.l,x8][[1]]; n = Solve[ eqn[9] /.a/.b/.c/.d/.e/.f/.l/.m,x9][[1]]; m = Solve[ eqn[8] /.n,x8][[1]] l = Solve[ eqn[7] /.n/.m,x7][[1]] f = Solve[ eqn[6] /.n/.m/.l,x6][[1]] e = Solve[ eqn[5] /.n/.m/.l/.f,x5][[1]] d = Solve[ eqn[4] /.n/.m/.l/.f/.e,x4][[1]] c = Solve[ eqn[3] /.n/.m/.l/.f/.e/.d,x3][[1]] b = Solve[ eqn[2] /.n/.m/.l/.f/.e/.d/.c,x2][[1]] a = Solve[ eqn[1] /.n/.m/.l/.f/.e/.d/.c/.b,x1][[1]] sol = x/.a/.b/.c/.d/.e/.f/.l/.m/.n In this way I obige Mathematica to simplify step by step the expression, avoiding the generation of too many terms. The problem is: it takes several days! Maybe someone of you know how to solve a simbolic system in efficient way, without generating enormous expressions? Thanks in advance F. Renzoni renzoni at fexphds04.tu-graz.ac.at