def covariance(x, mean_x, y, mean_y):
	"""
	This function calculates the co-variance of x and y
	Args:
		x (np array): array
		mean_x (float): mean of x array
		y (np array): array
		mean_y (float): mean of y array
	Returns:
		float: co-variance
	"""
	
	covar = 0.0
	for i in range(x.shape[1]):
		covar += (x[0][i]-mean_x) * (y[0][i]-mean_y)
	return covar