C Procedury na reseni nelinearnich rovnic.

      REAL FUNCTION SUCFAI(F,X,DX0,EPS,NMAX)
C Rosenbrockova metoda "success - failure"
      INTEGER NMAX
      REAL F,X,DX0,EPS
      EXTERNAL F
      
      DOUBLE PRECISION ALFA,BETA,F1,F2,F3,T,S1,S2,A,DX
      REAL X0,X1,X2,X3
      INTEGER J
      DATA ALFA/1.5/,BETA/0.5/

      DX = DX0
      X1 = X
      F1 = F(X1)
      X2 = X1 + DX
      F2 = F(X2)
      IF( F2.LT.F1 )THEN
C Uspech
        DX = ALFA*DX
        T = X1
        X1 = X2
        X2 = T
        T = F1
        F1 = F2
        F2 = T
      ELSE
C Neuspech
        DX = -BETA*DX
      ENDIF
      DO J = 3,NMAX
        X3 = X1 + DX
        F3 = F(X3)
        IF( F3.LE.F1 )THEN
C Uspech
          X2 = X1
          F2 = F1
          X1 = X3
          F1 = F3
          DX = ALFA*DX
        ELSE
C Neuspech, kvadraticka interpolace
          S1 = (F1 - F2)*(X2 - X3)          
          S2 = (F2 - F3)*(X1 - X2)
          A = 2.0*(S2 - S1)
          X0 = (S2*(X1 + X2) - S1*(X2 + X3))/A
          A = A/((X3 - X2)*(X2 - X1)*(X3 - X1))
          X2 = X1
          F2 = F1
          X1 = X0
          F1 = F(X1)
          DX = X1 - X2
          IF( F1.GT.F2 )THEN
            DX = -BETA*DX
            T = X1
            X1 = X2
            X2 = T
            T = F1
            F1 = F2
            F2 = T
          ENDIF   
        ENDIF
        IF( ABS(DX).LT.EPS ) THEN
          SUCFAI = F1
          X = X1
          RETURN
        ENDIF
      ENDDO
      SUCFAI = 1E37
      END