Added activation functions: leaky_relu relu6 softplus elu celu logsigmoid (#108)

* added leaky_relu relu6 softplus elu celu logsigmoid
* minor fixes for docstring and benchmark imports
* fixed elu implementation and added tests
* added tests for optional param, changed leaky_relu param to fit pytorch documentation

python/mlx/nn/layers/__init__.py

@@ -1,14 +1,26 @@
 # Copyright © 2023 Apple Inc.
 
 from mlx.nn.layers.activations import (
+    CELU,
+    ELU,
     GELU,
+    LeakyReLU,
+    LogSigmoid,
     ReLU,
+    ReLU6,
     SiLU,
+    Softplus,
+    celu,
+    elu,
     gelu,
     gelu_approx,
     gelu_fast_approx,
+    leaky_relu,
+    log_sigmoid,
     relu,
+    relu6,
     silu,
+    softplus,
 )
 from mlx.nn.layers.base import Module
 from mlx.nn.layers.containers import Sequential

python/mlx/nn/layers/activations.py

@@ -32,6 +32,47 @@ def relu(x):
     return mx.maximum(x, 0)
 
 
+def leaky_relu(x, negative_slope=0.01):
+    """Applies the Leaky Rectified Linear Unit.
+
+    Simply ``mx.maximum(negative_slope * x, x)``.
+    """
+    return mx.maximum(negative_slope * x, x)
+
+
+def elu(x, alpha=1.0):
+    """Applies the Exponential Linear Unit.
+
+    Simply ``mx.where(x > 0, x, alpha * (mx.exp(x) - 1))``.
+    """
+    return mx.where(x > 0, x, alpha * (mx.exp(x) - 1))
+
+
+def relu6(x):
+    r"""Applies the Rectified Linear Unit 6.
+
+    Applies :math:`\min(\max(x, 0), 6)` element wise.
+    """
+    return mx.minimum(mx.maximum(x, 0), 6.0)
+
+
+def softplus(x):
+    r"""Applies the Softplus function.
+
+    Applies :math:`\log(1 + \exp(x))` element wise.
+    """
+    return mx.logaddexp(x, 0)
+
+
+def celu(x, alpha=1.0):
+    r"""Applies the Continuously Differentiable Exponential Linear Unit.
+
+    Applies :math:`\max(0, x) + \min(0, \alpha * (\exp(x / \alpha) - 1))`
+    element wise.
+    """
+    return mx.maximum(x, 0.0) + alpha * (mx.exp(mx.minimum(x, 0.0) / alpha) - 1)
+
+
 def silu(x):
     r"""Applies the Sigmoid Linear Unit.
 
@@ -41,6 +82,14 @@ def silu(x):
     return x * mx.sigmoid(x)
 
 
+def log_sigmoid(x):
+    r"""Applies the Log Sigmoid function.
+
+    Applies :math:`\log(\sigma(x)) = -\log(1 + e^{-x})` element wise.
+    """
+    return -softplus(-x)
+
+
 def gelu(x):
     r"""Applies the Gaussian Error Linear Units function.
 
@@ -99,11 +148,80 @@ class ReLU(Module):
     pass
 
 
+class LeakyReLU(Module):
+    r"""Applies the Leaky Rectified Linear Unit.
+
+    Simply ``mx.maximum(negative_slope * x, x)``.
+
+    Args:
+        negative_slope: Controls the angle of the negative slope. Default: 1e-2.
+    """
+
+    def __init__(self, negative_slope=1e-2):
+        super().__init__()
+        self._negative_slope = negative_slope
+
+    def __call__(self, x):
+        return leaky_relu(x, self._negative_slope)
+
+
+class ELU(Module):
+    r"""Applies the Exponential Linear Unit.
+        Simply ``mx.where(x > 0, x, alpha * (mx.exp(x) - 1))``.
+
+    See :func:`elu`, for the functional equivalent.
+
+    Args:
+        alpha: the :math:`\alpha` value for the ELU formulation. Default: 1.0
+    """
+
+    def __init__(self, alpha=1.0):
+        super().__init__()
+        self._alpha = alpha
+
+    def __call__(self, x):
+        return elu(x, self._alpha)
+
+
+@_make_activation_module(relu6)
+class ReLU6(Module):
+    pass
+
+
+@_make_activation_module(softplus)
+class Softplus(Module):
+    pass
+
+
+class CELU(Module):
+    r"""Applies the Continuously Differentiable Exponential Linear Unit.
+        Applies :math:`\max(0, x) + \min(0, \alpha * (\exp(x / \alpha) - 1))`
+        element wise.
+
+    See :func:`celu`, for the functional equivalent.
+
+    Args:
+        alpha: the :math:`\alpha` value for the CELU formulation. Default: 1.0
+    """
+
+    def __init__(self, alpha=1.0):
+        super().__init__()
+        self._alpha = alpha
+
+    def __call__(self, x):
+        return celu(x, self._alpha)
+
+
 @_make_activation_module(silu)
 class SiLU(Module):
     pass
 
 
+@_make_activation_module(log_sigmoid)
+class LogSigmoid(Module):
+    pass
+
+
 class GELU(Module):
     r"""Applies the Gaussian Error Linear Units.