import numpy as np


def zero_crossing(eod,time):
	threshold = 0
	shift_eod = np.roll(eod, 1)
	eod_times = time[(eod >= threshold) & (shift_eod < threshold)]
	sampling_rate = 40000.0
	eod_idx = eod_times*sampling_rate
	return eod_idx


def vector_strength(spike_times, eod_durations):
	alphas = spike_times/ eod_durations
	cs = (1/len(spike_times))*np.sum(np.cos(alphas))^2
	sn = (1/len(spike_times))*np.sum(np.sin(alphas))^2
	vs = np.sqrt(cs+sn)
	return vs