'Returns the i\'th point of a sequence.
If start point is negative infinity, point is returned from the end.
Assumes the first point to be indexed zero.
Examples
>>> from sympy import oo
>>> from sympy.series.sequences import SeqPer
bounded
>>> SeqPer((1, 2, 3), (-10, 10))._ith_point(0)
-10
>>> SeqPer((1, 2, 3), (-10, 10))._ith_point(5)
-5
End is at infinity
>>> SeqPer((1, 2, 3), (0, oo))._ith_point(5)
5
Starts at negative infinity
>>> SeqPer((1, 2, 3), (-oo, 0))._ith_point(5)
-5'

def _ith_point(self, i):

    if (self.start is S.NegativeInfinity):
        initial = self.stop
    else:
        initial = self.start
    if (self.start is S.NegativeInfinity):
        step = (-1)
    else:
        step = 1
    return (initial + (i * step))
