bessk1.pas

Delphi Pascal 数据挖掘领域算法包 数值算法大全

FUNCTION bessk1(x: real): real;
VAR
   y,ans: double;
BEGIN
   IF  (x <= 2.0)  THEN BEGIN
      y := x*x/4.0;
      ans := (ln(x/2.0)*bessi1(x))+(1.0/x)*(1.0+y*(0.15443144
         +y*(-0.67278579+y*(-0.18156897+y*(-0.1919402e-1
         +y*(-0.110404e-2+y*(-0.4686e-4)))))))  END
   ELSE BEGIN
      y := 2.0/x;
      ans := (exp(-x)/sqrt(x))*(1.25331414+y*(0.23498619
         +y*(-0.3655620e-1+y*(0.1504268e-1+y*(-0.780353e-2
         +y*(0.325614e-2+y*(-0.68245e-3)))))))  END;
   bessk1 := sngl(ans)
END;