C ===  Derivating with respect to: 
C     X Y                                                                  
C
      SUBROUTINE ROSENB (X, Y, F)
      IMPLICIT REAL*8 (A-H,O-Z)
C == Rosenbrock's function ==
      F_1=100.0*2*(Y-X*X)**(2-1)*(-X-X)+2*(1-X)**(2-1)*(-1.)
      F_2=100.0*2*(Y-X*X)**(2-1)
      F = 100.0 * (Y - X*X)**2 + (1 - X)**2
      RETURN
      END
