A=matrix([[4,2,14],[2,17,-5],[14,-5,83]])
//A=L*U where L is lower triangular matrix,U is transpose of L
//l11,l22,l21,l31,l32,l33 are elements in L,U
var('l33')   //declare all other variables
l11=sqrt(A[0,0])
l21=A[1,0]/l11
l31=A[2,0]/l11
l22=sqrt(A[1,1]-l21*l21)
l32=(A[2,1]-l31*l21)/l22
l33=sqrt(A[2,2]-l31*l31-l32*l32)
L=matrix([[l11,0,0],[l21,l22,0],[l31,l32,l33]])
U=L.transpose()
B=matrix([[14],[-101],[155]])
Y=L^(-1)*B
X=U^(-1)*Y
X
[ 3]
[-6]
[ 1]  //final solution

Kreyszig-18.2-2 (last edited 2010-12-17 12:22:47 by 172)