function R=trichol(A);
% TRICHOL Cholesky factorization for tridiagonal
% positive definite matrices.  Soln to F1(d) on 
% Math 630 Fall 2003 Final Exam.  ELB 12/18/03

m=size(A,1);
R=triu(A);
for k=1:m-1
    R(k+1,k+1)=R(k+1,k+1)-R(k,k+1)*R(k,k+1)/R(k,k);
    R(k,k)=sqrt(R(k,k));
    R(k,k+1)=R(k,k+1)/R(k,k);
end
R(m,m)=sqrt(R(m,m));