Jacobi Preconditioning

subroutine Jacobi (omega, x, b)

  [snip]

  type(JT_vector_type), intent(in) :: X

  ! Gather element face neighbors
  call EE_GATHER (X_Neighbors, X%Values, BOUNDARY=X%Aux1)

  ! Perform a matrix-vector multiply using coefficients
  ! from the orthogonal operator, except for the diagonal.
  Dot = zero
  do f = 1,nfc
     Dot = Dot + Ortho_Coeff(f,:) * X_Neighbors(f,:)
  end do

  ! Update iterate.
  Dot = (B - Dot) / Ortho_Coeff(0,:)
  X%Values = X%Values + omega*(Dot - X%Values)

  [snip]