2 csch - hyperbolic cosecant
9 eps nonzero real, defaults to epsilon()
14 Calculate the csch of x to a multiple of epsilon, with error less in
15 absolute value than .75 * eps.
17 csch(x) = 2/(exp(x) - exp(-x))
20 > print csch(1, 1e-5), csch(1, 1e-10), csch(1, 1e-15), csch(1, 1e-20)
21 .85092 .8509181282 .850918128239322 .85091812823932154513
27 NUMBER *qcsch(NUMBER *x, NUMBER *eps)
30 sinh, cosh, tanh, sech, coth, epsilon