subroutine pvBackSubst(A,n,p,b)
      implicit none
      integer n, j, p(n),nmax
      parameter(nmax=4)
      double complex A(n,n),b(n,-2:0)
      double complex xm2(nmax),xm1(nmax),xm0(nmax)
      if (n .gt. nmax) then
      write(6,*) 'Error in BackSubst, n .gt. nmax'
      stop
      endif
 
      do j=1,n
      xm2(j)=b(j,-2)
      xm1(j)=b(j,-1)
      xm0(j)=b(j, 0)
      enddo

      call XLUBackSubst(A, n, p, xm2)
      call XLUBackSubst(A, n, p, xm1)
      call XLUBackSubst(A, n, p, xm0)

      do j=1,n
      b(j,-2)=xm2(j)
      b(j,-1)=xm1(j)
      b(j, 0)=xm0(j)
      enddo

      return
      end