unit2.pas

1、说明： 本书中所有的常用数值算法子过程按书中的章数分别放在以C开头的子目录中。 所有这些为验证上述子过程而编的验证过程按书中的章数分别放在以D开头的子目录中。 所有为验

unit Unit2;

interface
Function BESSJ1(X:real):real;

implementation
Function BESSJ1(X:real):real;
var
    AAA,BBB,CCC,AX,Z,Y,XX,SGN:real;
const
    R1 = 72362614232;         R2 = -7895059235;
    R3 = 242396853.1;         R4 = -2972611.439;
    R5 = 15704.4826;          R6 = -30.16036606;
    S1 = 144725228442;        S2 = 2300535178;
    S3 = 18583304.74;         S4 = 99447.43394;
    S5 = 376.9991397;         S6 = 1;
    P1 = 1;                   P2 = 0.00183105;
    P3 = -0.3516396496e-4;    P4 = 0.000002457520174;
    P5 = -0.240337019e-6;
    Q1 = 0.04687499995;       Q2 = -0.2002690873e-3;
    Q3 = 0.8449199096e-5;     Q4 = -0.88228987e-6;
    Q5 = 0.105787412e-6;
begin
    If Abs(X) < 8 Then
    begin
        Y:=X * X;
        AAA:=R1 + Y * (R2 + Y * (R3 + Y * (R4 + Y * (R5 + Y * R6))));
        BBB:=S1 + Y * (S2 + Y * (S3 + Y * (S4 + Y * (S5 + Y * S6))));
        BESSJ1:=X * AAA / BBB;
    end
    Else
    begin
        AX:=Abs(X);
        Z:=8 / AX;
        Y:=Z * Z;
        XX:=AX - 2.356194491;
        AAA:=P1 + Y * (P2 + Y * (P3 + Y * (P4 + Y * P5)));
        BBB:=Q1 + Y * (Q2 + Y * (Q3 + Y * (Q4 + Y * Q5)));
        CCC:=Sqrt(0.636619772 / AX);
        if X > 0 Then
          SGN:= 1
        ELSE
          SGN:= -1;
        BESSJ1:=CCC * (Cos(XX) * AAA - Z * Sin(XX) * BBB * Sgn);
    end;
end;

end.