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fvn_fnlib/besk1.f
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function besk1 (x)
c july 1980 version. w. fullerton, c3, los alamos scientific lab.
dimension bk1cs(11)
external besi1, besk1e, csevl, inits, r1mach
c
c series for bk1 on the interval 0. to 4.00000d+00
c with weighted error 7.02e-18
c log weighted error 17.15
c significant figures required 16.73
c decimal places required 17.67
c
data bk1 cs( 1) / .0253002273 389477705e0 /
data bk1 cs( 2) / -.3531559607 76544876e0 /
data bk1 cs( 3) / -.1226111808 22657148e0 /
data bk1 cs( 4) / -.0069757238 596398643e0 /
data bk1 cs( 5) / -.0001730288 957513052e0 /
data bk1 cs( 6) / -.0000024334 061415659e0 /
data bk1 cs( 7) / -.0000000221 338763073e0 /
data bk1 cs( 8) / -.0000000001 411488392e0 /
data bk1 cs( 9) / -.0000000000 006666901e0 /
data bk1 cs(10) / -.0000000000 000024274e0 /
data bk1 cs(11) / -.0000000000 000000070e0 /
c
data ntk1, xmin, xsml, xmax /0, 0., 0., 0. /
c
if (ntk1.ne.0) go to 10
ntk1 = inits (bk1cs, 11, 0.1*r1mach(3))
xmin = exp (amax1(alog(r1mach(1)), -alog(r1mach(2))) + .01)
xsml = sqrt (4.0*r1mach(3))
xmax = -alog(r1mach(1))
xmax = xmax - 0.5*xmax*alog(xmax)/(xmax+0.5) - 0.01
c
10 if (x.le.0.) call seteru (29hbesk1 x is zero or negative, 29,
1 2, 2)
if (x.gt.2.0) go to 20
c
if (x.lt.xmin) call seteru (31hbesk1 x so small k1 overflows,
1 31, 3, 2)
y = 0.
if (x.gt.xsml) y = x*x
besk1 = alog(0.5*x)*besi1(x) +
1 (0.75 + csevl (.5*y-1., bk1cs, ntk1))/x
return
c
20 besk1 = 0.
if (x.gt.xmax) call seteru (30hbesk1 x so big k1 underflows,
1 30, 1, 0)
if (x.gt.xmax) return
c
besk1 = exp(-x) * besk1e(x)
c
return
end
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