"""
	Statistics module

	- mean
	- variance
	- standard deviation
	- min/max value

"""


def variance(l):
	a = std_deviation(l)
	return a*a


def std_deviation(l):
	"""
		The standard deviation is a measure of the degree 
		of dispersion of the data from the mean value.
	"""
	m = mean(l)
	n = len(l)
	s = 0
	for k in l:
		s += (k - m)
	s /= (n-1)
	return sqrt(s)


def mean(l):
	"""
		Calculate the mean value of the list l
	"""
	n = len(l)
	s = 0
	for k in l:
		s += k
	return s/n

def min_value(l):
	""" Return the min value of the list l """
	return min(l)

def max_value(l):
	""" Return the max value of the list l """
	return max(l)