anchor.diff:    type(scalar_field):: q_ed  !pv on edges
     type(scalar_field):: q_ed_exact  !pv on edges
     type(scalar_field):: q_ed_error  !pv on edges
  +  type(scalar_field):: zeta  !relative vorticity - on triangles
   
   
     type(scalar_field):: q_grad_ed  !grad pv on edges
  
positive.code:     eta%n=mesh%nt
      eta%pos=1
      eta%name="eta"
      allocate(eta%f(1:eta%n), stat=ist)
  
      if(test_lterror==1)then
        allocate(eta_exact%f(1:eta%n), stat=ist)
  
negative.code: 
      !Vorticity
      eta%f=0._r8
      zeta%f=0._r8
      eta_ed%f=0._r8
      q_tr%f=0._r8
      q_ed%f=0._r8
  