bessi1.txt

常用的数值算法的VB程序

Function BESSI1(X)
    P1 = 0.5:              P2 = 0.87890594
    P3 = 0.51498869:       P4 = 0.15084934
    P5 = 0.02658733:       P6 = 0.00301532
    P7 = 0.00032411
    Q1 = 0.39894228:       Q2 = -0.03988024
    Q3 = -0.00362018:      Q4 = 0.00163801
    Q5 = -0.01031555:      Q6 = 0.02282967
    Q7 = -0.02895312:      Q8 = 0.01787654
    Q9 = -0.00420059
    If Abs(X) < 3.75 Then
        Y = (X / 3.75) ^ 2
        AAA = Y * (P4 + Y * (P5 + Y * (P6 + Y * P7)))
        BESSI1 = X * (P1 + Y * (P2 + Y * (P3 + AAA)))
    Else
        AX = Abs(X)
        Y = 3.75 / AX
        AAA = Exp(AX) / Sqr(AX)
        BBB = Y * (Q5 + Y * (Q6 + Y * (Q7 + Y * (Q8 + Y * Q9))))
        BESSI1 = AAA * (Q1 + Y * (Q2 + Y * (Q3 + Y * (Q4 + BBB))))
    End If
End Function