bessj0.f90

FORTRANvisualfortran常用数值算法集及源码

FUNCTION bessj0(x)
REAL bessj0,x
REAL ax,xx,z
DOUBLE PRECISION p1,p2,p3,p4,p5,q1,q2,q3,q4,q5,&
       r1,r2,r3,r4,r5,r6,s1,s2,s3,s4,s5,s6,y
SAVE p1,p2,p3,p4,p5,q1,q2,q3,q4,q5,r1,r2,r3,r4,r5,r6,&
     s1,s2,s3,s4,s5,s6
DATA p1,p2,p3,p4,p5/1.d0,-.1098628627d-2,.2734510407d-4,&
     -.2073370639d-5,.2093887211d-6/, q1,q2,q3,q4,q5&
	 /-.1562499995d-1,.1430488765d-3,-.6911147651d-5,&
	 .7621095161d-6,-.934945152d-7/
DATA r1,r2,r3,r4,r5,r6/57568490574.d0,-13362590354.d0,&
     651619640.7d0,-11214424.18d0,77392.33017d0,&
	 -184.9052456d0/,s1,s2,s3,s4,s5,s6/57568490411.d0,&
	 1029532985.d0,9494680.718d0,59272.64853d0,&
	 267.8532712d0,1.d0/
if(abs(x)<8.) then
  y=x**2
  bessj0=(r1+y*(r2+y*(r3+y*(r4+y*(r5+y*r6)))))/&
         (s1+y*(s2+y*(s3+y*(s4+y*(s5+y*s6)))))
else
  ax=abs(x)
  z=8./ax
  y=z**2
  xx=ax-.785398164
  bessj0=sqrt(.636619772/ax)*(cos(xx)*(p1+y*(p2+y*&
         (p3+y*(p4+y*p5))))-z*sin(xx)*(q1+y*(q2+y*&
		 (q3+y*(q4+y*q5)))))
endif
END FUNCTION bessj0