bessk1.f90

FORTRANvisualfortran常用数值算法集及源码

FUNCTION bessk1(x)
REAL bessk1,x
!USES bessi1
REAL bessi1
DOUBLE PRECISION p1,p2,p3,p4,p5,p6,p7,&
                        q1,q2,q3,q4,q5,q6,q7,y
SAVE p1,p2,p3,p4,p5,p6,p7,q1,q2,q3,q4,q5,q6,q7
DATA p1,p2,p3,p4,p5,p6,p7/1.0d0,0.15443144d0,&
     -0.67278579d0,-0.18156897d0,-0.1919402d-1,&
	 -0.110404d-2,-0.4686d-4/
DATA q1,q2,q3,q4,q5,q6,q7/1.25331414d0,0.23498619d0,&
     -0.3655620d-1,0.1504268d-1,-0.780353d-2,&
	 0.325614d-2,-0.68245d-3/
if (x<=2.0) then
  y=x*x/4.0
  bessk1=(log(x/2.0)*bessi1(x))+(1.0/x)*(p1+y*&
         (p2+y*(p3+y*(p4+y*(p5+y*(p6+y*p7))))))
else
  y=2.0/x
  bessk1=(exp(-x)/sqrt(x))*(q1+y*(q2+y*(q3+y*(q4+&
         y*(q5+y*(q6+y*q7))))))
endif
END FUNCTION bessk1