bessj1.pas

Delphi Pascal 数据挖掘领域算法包 数值算法大全

FUNCTION bessj1(x: real): real;
VAR
   ax,xx,z: real;  y,ans,ans1,ans2: double;
FUNCTION sign(x: real): real;
   BEGIN
      IF x >= 0.0 THEN sign := 1.0
      ELSE sign := -1.0;
   END;
BEGIN
   IF (abs(x) < 8.0) THEN BEGIN
      y := sqr(x);
      ans1 := x*(72362614232.0+y*(-7895059235.0+y*(242396853.1
         +y*(-2972611.439+y*(15704.48260+y*(-30.16036606))))));
      ans2 := 144725228442.0+y*(2300535178.0+y*(18583304.74
         +y*(99447.43394+y*(376.9991397+y*1.0))));
      bessj1 := sngl(ans1/ans2)  END
   ELSE BEGIN
      ax := abs(x); z := 8.0/ax; y := sqr(z); xx := ax-2.356194491;
      ans1 := 1.0+y*(0.183105e-2+y*(-0.3516396496e-4
         +y*(0.2457520174e-5+y*(-0.240337019e-6))));
      ans2 := 0.04687499995+y*(-0.2002690873e-3
         +y*(0.8449199096e-5+y*(-0.88228987e-6+y*0.105787412e-6)));
      ans := sqrt(0.636619772/ax)*(cos(xx)*ans1
         -z*sin(xx)*ans2)*sign(x);
      bessj1 := sngl(ans)  END
END;