bessy0.pas

来自「Delphi Pascal 数据挖掘领域算法包 数值算法大全」· PAS 代码 · 共 23 行

FUNCTION bessy0(x: real): real;
VAR
   xx,z: real;  y,ans,ans1,ans2: double;
BEGIN
   IF (x < 8.0) THEN BEGIN
      y := sqr(x);
      ans1 := -2957821389.0+y*(7062834065.0+y*(-512359803.6
         +y*(10879881.29+y*(-86327.92757+y*228.4622733))));
      ans2 := 40076544269.0+y*(745249964.8+y*(7189466.438
         +y*(47447.26470+y*(226.1030244+y*1.0))));
      ans := (ans1/ans2)+0.636619772*bessj0(x)*ln(x);
      bessy0 := sngl(ans)  END
   ELSE BEGIN
      z := 8.0/x; y := sqr(z); xx := x-0.785398164;
      ans1 := 1.0+y*(-0.1098628627e-2+y*(0.2734510407e-4
         +y*(-0.2073370639e-5+y*0.2093887211e-6)));
      ans2 := -0.1562499995e-1+y*(0.1430488765e-3
         +y*(-0.6911147651e-5+y*(0.7621095161e-6+y*(-0.934945152e-7))));
      ans := sin(xx)*ans1+z*cos(xx)*ans2;
      ans := sqrt(0.636619772/x)*ans;
      bessy0 := sngl(ans)  END
END;