bessi0.pas

Delphi Pascal 数据挖掘领域算法包 数值算法大全

FUNCTION bessi0(x: real): real;
VAR
   ax: real;  y,ans: double;
BEGIN
   IF (abs(x) < 3.75) THEN BEGIN
      y := sqr(x/3.75);
      ans := 1.0+y*(3.5156229+y*(3.0899424+y*(1.2067492+y*
         (0.2659732+y*(0.360768e-1+y*0.45813e-2)))))  END
   ELSE BEGIN
      ax := abs(x);  y := 3.75/ax;
      ans := (exp(ax)/sqrt(ax))*(0.39894228+y*(0.1328592e-1
         +y*(0.225319e-2+y*(-0.157565e-2+y*(0.916281e-2
         +y*(-0.2057706e-1+y*(0.2635537e-1+y*(-0.1647633e-1
         +y*0.392377e-2))))))))  END;
   bessi0 := sngl(ans)
END;