title " "
     
  Select
    ngrid=20
    cubic
  
  Variables
     psi(0.1e2)
     pso(0.1e2)

  Definitions  
Q= IF (abs(x) < 0.75) then (USTEP((y+0.5)+0.001)-USTEP((y+0.5)-0.001)) + (USTEP((y-0.5)+0.001)-USTEP((y-0.5)-0.001)) ELSE 0
 
  Initial values
    psi =  0
    pso =  0

  Equations
     del2(psi) = pso
     del2(pso) = Q

  Boundaries
    Region 1 
      start (-1,-1)
      value(psi) = 0
      value(pso) = 0
      line to (1,-1)
      value(psi) = 0
      value(pso) = 0
      line to (1,-0.5)
      to (-1,-0.5)
      value(psi) = 0
      value(pso) = 0
      line to finish

    Region 2 
      start (-1,-0.5)
      line to (1,-0.5)
      value(psi) = 0
      value(pso) = 0
      line to (1,0.5)
      to (-1,0.5)
      value(psi) = 0
      value(pso) = 0
      line to finish

    Region 3 
      start (-1,0.5)
      line to (1,0.5)
      value(psi) = 0
      value(pso) = 0
      line to (1,1)
      value(psi) = 0
      value(pso) = 0
      line to (-1,1)
      value(psi) = 0
      value(pso) = 0
      line to finish
    
  monitors
    contour(pso)

  plots
    contour (psi)
    elevation(psi) from (0,-1) to (0,1)
    surface(psi)
    contour (pso)
    elevation(pso) from (0,-1) to (0,1)
    surface(pso)
    surface (Q)/* VIEWPOINT(3,0.5,15)*/
    elevation(Q) from (0,-1) to (0,1)
    elevation(Q) from (-1,0.5) to (1,0.5)
    
  end