plgndr.txt

常用的数值算法的VB程序

Function PLGNDR(L, M, X)
    If M < 0 Or M > L Or Abs(X) > 1# Then Print "bad arguments"
    PMM = 1#
    If M > 0 Then
        SOMX2 = Sqr((1# - X) * (1# + X))
        FACT = 1#
        For I = 1 To M
            PMM = -PMM * FACT * SOMX2
            FACT = FACT + 2#
        Next I
    End If
    If L = M Then
        PLGNDR = PMM
    Else
        PMMP1 = X * (2 * M + 1) * PMM
        If L = M + 1 Then
            PLGNDR = PMMP1
        Else
            For LL = M + 2 To L
                PLL = X * (2 * LL - 1) * PMMP1 - (LL + M - 1) * PMM
                PLL = PLL / (LL - M)
                PMM = PMMP1
                PMMP1 = PLL
            Next LL
            PLGNDR = PLL
        End If
    End If
End Function