2 pi - evaluate pi to specified accuracy
8 eps nonzero real, defaults to epsilon()
13 Returns a multiple of eps differing from the true value of pi by
14 less than 0.75 eps, and in nearly all cases by less than 0.5 eps.
17 > print pi(1e-5), pi(1e-10), pi(1e-15), pi(1e-20)
18 3.14159 3.1415926536 3.141592653589793 3.14159265358979323846
24 NUMBER *qpi(NUMBER *eps)