anchor.diff:  
       double precision x,y
   
  +    INTEGER example
  +    COMMON /comm_example/ example
  +
       integer flag
       double precision q,qlap,b, grad_q(2), grad_beta(2)
   
       CALL poisson_fort_beta(x,y,b,grad_beta)
   
       flag = 2
  -    CALL poisson_qexact_complete(x,y,q,qlap,grad_q,flag)
  +    CALL poisson_qexact_complete(example,x,y,q,qlap,grad_q,flag)
   
       poisson_qexact_rhs = grad_beta(1)*grad_q(1) +  grad_beta(2)*grad_q(2) + b*qlap
   
  
positive.code: 
  
  
  SUBROUTINE poisson_qexact_complete(x,y,q,qlap,grad,flag)
      use hsmooth_mod, only : m_polar, x0_polar, y0_polar
      IMPLICIT NONE
  
      DOUBLE PRECISION x,y, q, qlap, grad(2)
      INTEGER flag
  
      INTEGER example
      COMMON /comm_example/ example
  
      DOUBLE PRECISION alpha,x0,y0,a,b
      COMMON /comm_rhs/ alpha,x0,y0,a,b
  
negative.code: 
      DOUBLE PRECISION x,y
      
      INTEGER example
      COMMON /comm_example/ example
  
      INTEGER flag
      DOUBLE PRECISION grad(2), q, qlap
  
  
      flag = 0  !! Don't compute the gradient
      call poisson_qexact_complete(example, x,y,q,qlap,grad,flag)
  
      poisson_qexact = q
  
  