mnbrak.f

      SUBROUTINE MNBRAK(AX,BX,CX,FA,FB,FC,FUNC)
      PARAMETER (GOLD=1.618034, GLIMIT=100., TINY=1.E-20)
      FA=FUNC(AX)
      FB=FUNC(BX)
      IF(FB.GT.FA)THEN
        DUM=AX
        AX=BX
        BX=DUM
        DUM=FB
        FB=FA
        FA=DUM
      ENDIF
      CX=BX+GOLD*(BX-AX)
      FC=FUNC(CX)
1     IF(FB.GE.FC)THEN
        R=(BX-AX)*(FB-FC)
        Q=(BX-CX)*(FB-FA)
        U=BX-((BX-CX)*Q-(BX-AX)*R)/(2.*SIGN(MAX(ABS(Q-R),TINY),Q-R))
        ULIM=BX+GLIMIT*(CX-BX)
        IF((BX-U)*(U-CX).GT.0.)THEN
          FU=FUNC(U)
          IF(FU.LT.FC)THEN
            AX=BX
            FA=FB
            BX=U
            FB=FU
            GO TO 1
          ELSE IF(FU.GT.FB)THEN
            CX=U
            FC=FU
            GO TO 1
          ENDIF
          U=CX+GOLD*(CX-BX)
          FU=FUNC(U)
        ELSE IF((CX-U)*(U-ULIM).GT.0.)THEN
          FU=FUNC(U)
          IF(FU.LT.FC)THEN
            BX=CX
            CX=U
            U=CX+GOLD*(CX-BX)
            FB=FC
            FC=FU
            FU=FUNC(U)
          ENDIF
        ELSE IF((U-ULIM)*(ULIM-CX).GE.0.)THEN
          U=ULIM
          FU=FUNC(U)
        ELSE
          U=CX+GOLD*(CX-BX)
          FU=FUNC(U)
        ENDIF
        AX=BX
        BX=CX
        CX=U
        FA=FB
        FB=FC
        FC=FU
        GO TO 1
      ENDIF
      RETURN
      END