fpback.f90

      subroutine fpback(a,z,n,k,c,nest)
!c  subroutine fpback calculates the solution of the system of
!c  equations a*c = z with a a n x n upper triangular matrix
!c  of bandwidth k.
!c  ..
!c  ..scalar arguments..
      integer n,k,nest
!c  ..array arguments..
      double precision a(nest,k),z(n),c(n)
!c  ..local scalars..
      double precision store

      integer i,i1,j,k1,l,m
!c  ..
      k1 = k-1
      c(n) = z(n)/a(n,1)
      i = n-1
      if(i.eq.0) go to 30
      do 20 j=2,n
        store = z(i)
        i1 = k1
        if(j.le.k1) i1 = j-1
        m = i
        do 10 l=1,i1
          m = m+1
          store = store-c(m)*a(i,l+1)
  10    continue
        c(i) = store/a(i,1)
        i = i-1
  20  continue
  30  return
      end