"""
activation functions
"""

# tanh:
# g(z) = tanh(z) = (exp(z) - exp(-z))/(exp(z) + exp(-z))
# g'(z) = 1 - (tanh(z))**2

# ReLU
def ReLU(z):
    return max((0, z))

def ReLUprime(z):
    return 1. if z > 0 else 0.