bessj0.pas

来自「Delphi Pascal 数据挖掘领域算法包 数值算法大全」· PAS 代码 · 共 22 行

FUNCTION bessj0(x: real): real;
VAR
   ax,xx,z: real;  y,ans,ans1,ans2: double;
BEGIN
   IF (abs(x) < 8.0) THEN BEGIN
      y := sqr(x);
      ans1 := 57568490574.0+y*(-13362590354.0+y*(651619640.7
         +y*(-11214424.18+y*(77392.33017+y*(-184.9052456)))));
      ans2 := 57568490411.0+y*(1029532985.0+y*(9494680.718
         +y*(59272.64853+y*(267.8532712+y*1.0))));
      bessj0 := sngl(ans1/ans2)  END
   ELSE BEGIN
      ax := abs(x); z := 8.0/ax; y := sqr(z); xx := ax-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 := sqrt(0.636619772/ax)*(cos(xx)*ans1-z*sin(xx)*ans2);
      bessj0 := sngl(ans)  END
END;