bessk0.pas

来自「Delphi Pascal 数据挖掘领域算法包 数值算法大全」· PAS 代码 · 共 17 行

FUNCTION bessk0(x: real): real;
VAR
   y,ans: double;
BEGIN
   IF (x <= 2.0) THEN BEGIN
      y := x*x/4.0;
      ans := (-ln(x/2.0)*bessi0(x))+(-0.57721566+y*(0.42278420
         +y*(0.23069756+y*(0.3488590e-1+y*(0.262698e-2
         +y*(0.10750e-3+y*0.74e-5))))))  END
   ELSE BEGIN
      y := (2.0/x);
      ans := (exp(-x)/sqrt(x))*(1.25331414+y*(-0.7832358e-1
         +y*(0.2189568e-1+y*(-0.1062446e-1+y*(0.587872e-2
         +y*(-0.251540e-2+y*0.53208e-3))))))  END;
   bessk0 := sngl(ans)
END;