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fvn_fnlib/besk0e.f
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function besk0e (x)
c july 1980 version. w. fullerton, c3, los alamos scientific lab.
dimension bk0cs(11), ak0cs(17), ak02cs(14)
external besi0, csevl, inits, r1mach
c
c series for bk0 on the interval 0. to 4.00000d+00
c with weighted error 3.57e-19
c log weighted error 18.45
c significant figures required 17.99
c decimal places required 18.97
c
data bk0 cs( 1) / -.0353273932 3390276872e0 /
data bk0 cs( 2) / .3442898999 246284869e0 /
data bk0 cs( 3) / .0359799365 1536150163e0 /
data bk0 cs( 4) / .0012646154 1144692592e0 /
data bk0 cs( 5) / .0000228621 2103119451e0 /
data bk0 cs( 6) / .0000002534 7910790261e0 /
data bk0 cs( 7) / .0000000019 0451637722e0 /
data bk0 cs( 8) / .0000000000 1034969525e0 /
data bk0 cs( 9) / .0000000000 0004259816e0 /
data bk0 cs(10) / .0000000000 0000013744e0 /
data bk0 cs(11) / .0000000000 0000000035e0 /
c
c series for ak0 on the interval 1.25000d-01 to 5.00000d-01
c with weighted error 5.34e-17
c log weighted error 16.27
c significant figures required 14.92
c decimal places required 16.89
c
data ak0 cs( 1) / -.0764394790 3327941e0 /
data ak0 cs( 2) / -.0223565260 5699819e0 /
data ak0 cs( 3) / .0007734181 1546938e0 /
data ak0 cs( 4) / -.0000428100 6688886e0 /
data ak0 cs( 5) / .0000030817 0017386e0 /
data ak0 cs( 6) / -.0000002639 3672220e0 /
data ak0 cs( 7) / .0000000256 3713036e0 /
data ak0 cs( 8) / -.0000000027 4270554e0 /
data ak0 cs( 9) / .0000000003 1694296e0 /
data ak0 cs(10) / -.0000000000 3902353e0 /
data ak0 cs(11) / .0000000000 0506804e0 /
data ak0 cs(12) / -.0000000000 0068895e0 /
data ak0 cs(13) / .0000000000 0009744e0 /
data ak0 cs(14) / -.0000000000 0001427e0 /
data ak0 cs(15) / .0000000000 0000215e0 /
data ak0 cs(16) / -.0000000000 0000033e0 /
data ak0 cs(17) / .0000000000 0000005e0 /
c
c series for ak02 on the interval 0. to 1.25000d-01
c with weighted error 2.34e-17
c log weighted error 16.63
c significant figures required 14.67
c decimal places required 17.20
c
data ak02cs( 1) / -.0120186982 6307592e0 /
data ak02cs( 2) / -.0091748526 9102569e0 /
data ak02cs( 3) / .0001444550 9317750e0 /
data ak02cs( 4) / -.0000040136 1417543e0 /
data ak02cs( 5) / .0000001567 8318108e0 /
data ak02cs( 6) / -.0000000077 7011043e0 /
data ak02cs( 7) / .0000000004 6111825e0 /
data ak02cs( 8) / -.0000000000 3158592e0 /
data ak02cs( 9) / .0000000000 0243501e0 /
data ak02cs(10) / -.0000000000 0020743e0 /
data ak02cs(11) / .0000000000 0001925e0 /
data ak02cs(12) / -.0000000000 0000192e0 /
data ak02cs(13) / .0000000000 0000020e0 /
data ak02cs(14) / -.0000000000 0000002e0 /
c
data ntk0, ntak0, ntak02, xsml / 3*0, 0. /
c
if (ntk0.ne.0) go to 10
ntk0 = inits (bk0cs, 11, 0.1*r1mach(3))
ntak0 = inits (ak0cs, 17, 0.1*r1mach(3))
ntak02 = inits (ak02cs, 14, 0.1*r1mach(3))
xsml = sqrt (4.0*r1mach(3))
c
10 if (x.le.0.) call seteru (29hbesk0e x is zero or negative, 29,
1 1, 2)
if (x.gt.2.) go to 20
c
y = 0.
if (x.gt.xsml) y = x*x
besk0e = exp(x) * (-alog(0.5*x)*besi0(x)
1 - .25 + csevl (.5*y-1., bk0cs, ntk0) )
return
c
20 if (x.le.8.) besk0e = (1.25 + csevl ((16./x-5.)/3., ak0cs, ntak0))
1 / sqrt(x)
if (x.gt.8.) besk0e = (1.25 + csevl (16./x-1., ak02cs, ntak02))
1 / sqrt(x)
c
return
end
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