import tensorflow as tf
def _softplus(x):
return tf.log1p(tf.exp(x))
def shifted_softplus(x):
"""
Softplus nonlinearity shifted by -log(2) such that shifted_softplus(0.) = 0.
y = log(0.5e^x + 0.5)
"""
y = tf.where(x < 14., _softplus(tf.where(x < 14., x, tf.zeros_like(x))), x)
return y - tf.log(2.)