bessk0.f90

FORTRANvisualfortran常用数值算法集及源码

FUNCTION bessk0(x)
REAL bessk0,x
!USES bessi0
REAL bessi0
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/-0.57721566d0,0.42278420d0,&
  0.23069756d0,0.3488590d-1,0.262698d-2,0.10750d-3,0.74d-5/
DATA q1,q2,q3,q4,q5,q6,q7/1.25331414d0,-0.7832358d-1,&
  0.2189568d-1,-0.1062446d-1,0.587872d-2,-0.251540d-2,&
  0.53208d-3/
if (x<=2.0) then
  y=x*x/4.0
  bessk0=(-log(x/2.0)*bessi0(x))+(p1+y*(p2+y*(p3+y*&
         (p4+y*(p5+y*(p6+y*p7))))))
else
  y=(2.0/x)
  bessk0=(exp(-x)/sqrt(x))*(q1+y*(q2+y*(q3+y*(q4+y*&
         (q5+y*(q6+y*q7))))))
endif
END FUNCTION bessk0