ccot.f
1.57 KB
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complex function ccot (z)
c march 1979 edition. w. fullerton, c3, los alamos scientific lab.
complex z
external r1mach
c 1 sqrt, tanh
data eps, xmax, ylarge, ybig, rmin, ymin / 5*0.0, 1.5 /
c
if (eps.ne.0.0) go to 10
eps = r1mach(4)
xmax = 1.0/eps
ylarge = -0.5*alog(0.5*r1mach(3))
ybig = -0.5*alog(0.5*sqrt(r1mach(3)))
rmin = exp (amax1(alog(r1mach(1)), -alog(r1mach(2))) + 0.01)
c
10 x = real (z)
y = aimag (z)
if (abs(y).gt.ylarge) go to 30
c
x2 = 2.0*x
y2 = 2.0*y
if (abs(x2).gt.xmax) go to 20
if (cabs(z).lt.rmin) call seteru (55hccot cabs(z) is zero or so
1 small that ccot overflows, 55, 5, 2)
c
call entsrc (irold, 1)
sn2x = sin(x2)
call erroff
den = cosh(y2) - cos(x2)
call erroff
call entsrc (irold2, irold)
c
if (den.lt.x*x2*eps*eps) call seteru (74hccot cot is nearly sin
1gular, x is near a multiple of pi and y is near 0, 74, 3, 2)
if (den.lt.x*x2*eps .and. abs(x).gt.0.5) call seteru (65hccot a
1nswer is lt half precision, x is near pi and y is near 0, 65, 1,1)
c
ccot = cmplx (sn2x/den, -sinh(y2)/den)
return
c
20 if (abs(y).lt.ymin) call seteru (75hccot answer would have no p
1recision, abs(x) is very big and abs(y) small, 75, 4, 2)
if (abs(y).lt.ybig) call seteru (69hccot answer lt half precisi
1on, abs(x) is very big and abs(y) small, 69, 2, 1)
c
ccot = cmplx (0.0, 1.0/tanh(y2))
return
c
30 ccot = cmplx (0.0, sign (1.0, y))
return
c
end