#!/usr/bin/env python3
from math import sqrt
def ave_error(arr):
M = len(arr)
assert(M>0)
if M == 1:
average = arr[0]
error = 0.
else:
average = sum(arr)/M
variance = 1./(M-1) * sum( [ (x - average)**2 for x in arr ] )
error = sqrt(variance/M)
return (average, error)