r9lgmc.f
1.47 KB
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function r9lgmc (x)
c august 1977 edition. w. fullerton, c3, los alamos scientific lab.
c
c compute the log gamma correction factor for x .ge. 10.0 so that
c alog (gamma(x)) = alog(sqrt(2*pi)) + (x-.5)*alog(x) - x + r9lgmc(x)
c
dimension algmcs(6)
external csevl,inits, r1mach
c
c series for algm on the interval 0. to 1.00000d-02
c with weighted error 3.40e-16
c log weighted error 15.47
c significant figures required 14.39
c decimal places required 15.86
c
data algmcs( 1) / .1666389480 45186e0 /
data algmcs( 2) / -.0000138494 817606e0 /
data algmcs( 3) / .0000000098 108256e0 /
data algmcs( 4) / -.0000000000 180912e0 /
data algmcs( 5) / .0000000000 000622e0 /
data algmcs( 6) / -.0000000000 000003e0 /
c
data nalgm, xbig, xmax / 0, 2*0.0 /
c
if (nalgm.ne.0) go to 10
nalgm = inits (algmcs, 6, r1mach(3))
xbig = 1.0/sqrt(r1mach(3))
xmax = exp (amin1(alog(r1mach(2)/12.0), -alog(12.0*r1mach(1))) )
c
10 if (x.lt.10.0) call seteru (23hr9lgmc x must be ge 10, 23, 1, 2)
if (x.ge.xmax) go to 20
c
r9lgmc = 1.0/(12.0*x)
if (x.lt.xbig) r9lgmc = csevl (2.0*(10./x)**2-1., algmcs, nalgm)/x
return
c
20 r9lgmc = 0.0
call seteru (34hr9lgmc x so big r9lgmc underflows, 34, 2, 0)
return
c
end