*-- Author : I.O. Skillicorn
      FUNCTION FPARAB(Z,X1,X2,X3,Z1,Z2,Z3)
C     CALCULATE X FOR Z ON PARABOLA THRU X1,X2,X3,Z1,Z2,Z3                                                    
      X=(Z-Z2)*(Z-Z3)/((Z1-Z2)*(Z1-Z3))*X1                              
      X=X+(Z-Z1)*(Z-Z3)/((Z2-Z1)*(Z2-Z3))*X2                            
      X=X+(Z-Z1)*(Z-Z2)/((Z3-Z1)*(Z3-Z2))*X3                            
      FPARAB=X                                                          
      RETURN                                                            
      END                                                               
*