sparse matrices

Dear mechanicians,



I'am a phd researcher on the field of
computational mechanics. I want to solve a linear system of equations [A]
{x} = {b} with PCG method. With the help of a very illuminating
book "Iterative Methods for Sparse Linear Systems" by Yousef Saad, I manage to
write an algorithm in Fortran90 language. But i have one problem... I
store A matrix in symmetric skyline format (upper triangular). I