mnbrak.txt

常用的数值算法的VB程序

Sub MNBRAK(AX, BX, CX, FA, FB, FC)
    GOLD = 1.618034
    GLIMIT = 100
    TINY = 1E-20
    FA = FUNC(AX)
    FB = FUNC(BX)
    If FB > FA Then
        DUM = AX
        AX = BX
        BX = DUM
        DUM = FB
        FB = FA
        FA = DUM
    End If
    CX = BX + GOLD * (BX - AX)
    FC = FUNC(CX)
1   If FB >= FC Then
        R = (BX - AX) * (FB - FC)
        Q = (BX - CX) * (FB - FA)
        DUM = Q - R
        If Abs(DUM) < TINY Then DUM = TINY
        U = BX - ((BX - CX) * Q - (BX - AX) * R) / (2 * DUM)
        ULIM = BX + GLIMIT * (CX - BX)
        If (BX - U) * (U - CX) > 0 Then
            FU = FUNC(U)
            If FU < FC Then
                AX = BX
                FA = FB
                BX = U
                FB = FU
                Exit Sub
            ElseIf FU > FB Then
                CX = U
                FC = FU
                Exit Sub
            End If
            U = CX + GOLD * (CX - BX)
            FU = FUNC(U)
        ElseIf (CX - U) * (U - ULIM) > 0 Then
            FU = FUNC(U)
            If FU < FC Then
                BX = CX
                CX = U
                U = CX + GOLD * (CX - BX)
                FB = FC
                FC = FU
                FU = FUNC(U)
            End If
        ElseIf (U - ULIM) * (ULIM - CX) >= 0 Then
            U = ULIM
            FU = FUNC(U)
        Else
            U = CX + GOLD * (CX - BX)
            FU = FUNC(U)
        End If
        AX = BX
        BX = CX
        CX = U
        FA = FB
        FB = FC
        FC = FU
        GoTo 1
    End If
End Sub