description:
log ket
log[t] ket
logarithm of x
if x <= 0, return 0
if t is None, return math.log(x) (ie, base e)
else, return math.log(x, t) (ie, base t)
examples:
log 2.71828|e>
1.0|e>
log[10] 100000 |x>
5|x>
see also: