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