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fvn_fnlib/besi1.f
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function besi1 (x)
c oct 1983 version. w. fullerton, c3, los alamos scientific lab.
dimension bi1cs(11)
external besi1e, csevl, inits, r1mach
c
c series for bi1 on the interval 0. to 9.00000d+00
c with weighted error 2.40e-17
c log weighted error 16.62
c significant figures required 16.23
c decimal places required 17.14
c
data bi1 cs( 1) / -.0019717132 61099859e0 /
data bi1 cs( 2) / .4073488766 7546481e0 /
data bi1 cs( 3) / .0348389942 99959456e0 /
data bi1 cs( 4) / .0015453945 56300123e0 /
data bi1 cs( 5) / .0000418885 21098377e0 /
data bi1 cs( 6) / .0000007649 02676483e0 /
data bi1 cs( 7) / .0000000100 42493924e0 /
data bi1 cs( 8) / .0000000000 99322077e0 /
data bi1 cs( 9) / .0000000000 00766380e0 /
data bi1 cs(10) / .0000000000 00004741e0 /
data bi1 cs(11) / .0000000000 00000024e0 /
c
c
data nti1, xmin, xsml, xmax / 0, 3*0. /
c
if (nti1.ne.0) go to 10
nti1 = inits (bi1cs, 11, 0.1*r1mach(3))
xmin = 2.0*r1mach(1)
xsml = sqrt (8.0*r1mach(3))
xmax = alog (r1mach(2))
c
10 y = abs(x)
if (y.gt.3.0) go to 20
c
besi1 = 0.0
if (y.eq.0.0) return
c
if (y.le.xmin) call seteru (
1 37hbesi1 abs(x) so small i1 underflows, 37, 1, 0)
if (y.gt.xmin) besi1 = 0.5*x
if (y.gt.xsml) besi1 = x * (.875 + csevl(y*y/4.5-1., bi1cs, nti1))
return
c
20 if (y.gt.xmax) call seteru (
1 34hbesi1 abs(x) so big i1 overflows, 34, 2, 2)
c
besi1 = exp(y) * besi1e(x)
c
return
end
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