bessi0.txt

Visual Basic 常用数学算法集书中收录了所有代码

Function BESSI0(X)
    P1 = 1#:              P2 = 3.5156229
    P3 = 3.0899424:       P4 = 1.2067492
    P5 = 0.2659732:       P6 = 0.0360768
    P7 = 0.0045813
    Q1 = 0.39894228:      Q2 = 0.01328592
    Q3 = 0.00225319:      Q4 = -0.00157565
    Q5 = 0.00916281:      Q6 = -0.02057706
    Q7 = 0.02635537:      Q8 = -0.01647633
    Q9 = 0.00392377
    If Abs(X) < 3.75 Then
        Y = (X / 3.75) ^ 2
        AAA = Y * (P5 + Y * (P6 + Y * P7))
        BESSI0 = P1 + Y * (P2 + Y * (P3 + Y * (P4 + AAA)))
    Else
        AX = Abs(X)
        Y = 3.75 / AX
        AAA = Exp(AX) / Sqr(AX)
        BBB = Q4 + Y * (Q5 + Y * (Q6 + Y * (Q7 + Y * (Q8 + Y * Q9))))
        BESSI0 = AAA * (Q1 + Y * (Q2 + Y * (Q3 + Y * BBB)))
    End If
End Function