message: added explanation for tanh, sigmoid, linear and exponential activation function
diff: @@ -165,16 +165,40 @@ def relu(x, alpha=0., max_value=None, threshold=0):
  @keras_export('keras.activations.tanh')
  def tanh(x):
  + """Hyperbolic Tangent activation function.
  +
  + Arguments:
  + x: Input tensor.
  +
  + Returns:
  + The tanh activation: `tanh(x) = sinh(x)/cosh(x) = ((exp(x) - exp(-x))/(exp(x) + exp(-x)))`.
  + """
  return nn.tanh(x)
  @keras_export('keras.activations.sigmoid')
  def sigmoid(x):
  + """Sigmoid activation function.
  +
  + Arguments:
  + x: Input tensor.
  +
  + Returns:
  + The sigmoid activation: `(1.0 / (1.0 + exp(-x)))`.
  + """
  return nn.sigmoid(x)
  @keras_export('keras.activations.exponential')
  def exponential(x):
  + """Exponential activation function.
  +
  + Arguments:
  + x: Input tensor.
  +
  + Returns:
  + The exponential activation: `exp(x)`.
  + """
  return math_ops.exp(x)
  @@ -198,6 +222,14 @@ def hard_sigmoid(x):
  @keras_export('keras.activations.linear')
  def linear(x):
  + """Linear activation function.
  +
  + Arguments:
  + x: Input tensor.
  +
  + Returns:
  + The linear activation: `x`.
  + """
  return x
  