1、sigmoid
tf.sigmoid(x, name = None)
y = 1/(1 + exp(-x))
2、tanh
tf.tanh(x, name = None)
tanh(x) = sinh(x)/cosh(x) = (exp(x) - exp(-x)) / (exp(x) + exp(-x))
3、relu
tf.nn.relu(x, name = None)
relu(x) = max(0, x)
4、relu6
tf.nn.relu6(x, name = None)
relu6(x) = min(max(x, 0), 6)
5、elu
tf.nn.elu(x, name = None)
6、softplus
tf.nn.softplus(features, name = None)
softplkus(x) = log(exp(feature) + 1)
7、softsign
tf.nn.softsign(x, name = None)
softsign(x) = x / abs(x+ 1)