bessk0.txt

常用的数值算法的VB程序

Function BESSK0(X)
    P1 = -0.57721566:      P2 = 0.4227842
    P3 = 0.23069756:       P4 = 0.0348859
    P5 = 0.00262698:       P6 = 0.0001075
    P7 = 0.0000074:
    Q1 = 1.25331414:       Q2 = -0.07832358:
    Q3 = 0.02189568:       Q4 = -0.01062446
    Q5 = 0.00587872:       Q6 = -0.0025154
    Q7 = 0.00053208
    If X <= 2# Then
        Y# = X * X / 4#
        BBB = Y * (P5 + Y * (P6 + Y * P7))
        AAA# = P1 + Y * (P2 + Y * (P3 + Y * (P4 + BBB)))
        BESSK0 = (-Log(X / 2#) * BESSI0(X)) + AAA#
    Else
        Y# = (2# / X)
        BBB = Y * (Q5 + Y * (Q6 + Y * Q7))
        AAA# = Q1 + Y * (Q2 + Y * (Q3 + Y * (Q4 + BBB)))
        BESSK0 = (Exp(-X) / Sqr(X)) * AAA#
    End If
End Function