Add jax.nn.mish.

docs/jax.nn.rst

@@ -38,6 +38,7 @@ Activation functions
     gelu
     glu
     squareplus
+    mish
 
 Other functions
 ---------------

jax/_src/nn/functions.py

@@ -199,6 +199,29 @@ def silu(x: ArrayLike) -> Array:
 
 swish = silu
 
+@jax.jit
+def mish(x: ArrayLike) -> Array:
+  r"""Mish activation function.
+
+  Computes the element-wise function:
+
+  .. math::
+    \mathrm{mish}(x) = x \cdot \mathrm{tanh}(\mathrm{softplus}(x))
+
+  For more information, see
+  `Mish: A Self Regularized Non-Monotonic Activation Function
+  <https://arxiv.org/abs/1908.08681>`_.
+
+  Args:
+    x : input array
+
+  Returns:
+    An array.
+  """
+  numpy_util.check_arraylike("mish", x)
+  x_arr = jnp.asarray(x)
+  return x_arr * jnp.tanh(softplus(x_arr))
+
 @jax.jit
 def log_sigmoid(x: ArrayLike) -> Array:
   r"""Log-sigmoid activation function.
@@ -314,7 +337,7 @@ def celu(x: ArrayLike, alpha: ArrayLike = 1.0) -> Array:
 
   For more information, see
   `Continuously Differentiable Exponential Linear Units
-  <https://arxiv.org/pdf/1704.07483.pdf>`_.
+  <https://arxiv.org/abs/1704.07483>`_.
 
   Args:
     x : input array
@@ -342,7 +365,7 @@ def selu(x: ArrayLike) -> Array:
 
   For more information, see
   `Self-Normalizing Neural Networks
-  <https://papers.nips.cc/paper/6698-self-normalizing-neural-networks.pdf>`_.
+  <https://arxiv.org/abs/1706.02515>`_.
 
   Args:
     x : input array

jax/nn/__init__.py

@@ -45,6 +45,7 @@ from jax._src.nn.functions import (
   silu as silu,
   swish as swish,
   squareplus as squareplus,
+  mish as mish,
 )
 
 # Deprecations

tests/nn_test.py

@@ -91,6 +91,26 @@ class NNFunctionsTest(jtu.JaxTestCase):
   def testSquareplusZero(self, dtype):
     self.assertEqual(dtype(1), nn.squareplus(dtype(0), dtype(4)))
 
+  def testMishGrad(self):
+    check_grads(nn.mish, (1e-8,), order=4,
+                rtol=1e-2 if jtu.test_device_matches(["tpu"]) else None)
+
+  def testMishGradZero(self):
+    check_grads(nn.mish, (0.,), order=1,
+                rtol=1e-2 if jtu.test_device_matches(["tpu"]) else None)
+
+  def testMishGradNegInf(self):
+    check_grads(nn.mish, (-float('inf'),), order=1,
+                rtol=1e-2 if jtu.test_device_matches(["tpu"]) else None)
+
+  def testMishGradNan(self):
+    check_grads(nn.mish, (float('nan'),), order=1,
+                rtol=1e-2 if jtu.test_device_matches(["tpu"]) else None)
+
+  @parameterized.parameters([float] + jtu.dtypes.floating)
+  def testMishZero(self, dtype):
+    self.assertEqual(dtype(0), nn.mish(dtype(0)))
+
   def testReluGrad(self):
     rtol = 1e-2 if jtu.test_device_matches(["tpu"]) else None
     check_grads(nn.relu, (1.,), order=3, rtol=rtol)
@@ -117,6 +137,10 @@ class NNFunctionsTest(jtu.JaxTestCase):
     val = nn.squareplus(1e3)
     self.assertAllClose(val, 1e3, check_dtypes=False, atol=1e-3)
 
+  def testMishValue(self):
+    val = nn.mish(1e3)
+    self.assertAllClose(val, 1e3, check_dtypes=False, atol=1e-3)
+
   @jtu.skip_on_flag("jax_skip_slow_tests", True)
   def testEluGrad(self):
     check_grads(nn.elu, (1e4,), order=4, eps=1.)
@@ -149,7 +173,7 @@ class NNFunctionsTest(jtu.JaxTestCase):
       (jnp.float32, jnp.bfloat16, jnp.float16),
       (partial(nn.gelu, approximate=False),
        partial(nn.gelu, approximate=True),
-       nn.relu, nn.softplus, nn.sparse_plus, nn.sigmoid, nn.squareplus)))
+       nn.relu, nn.softplus, nn.sparse_plus, nn.sigmoid, nn.squareplus, nn.mish)))
   def testDtypeMatchesInput(self, dtype, fn):
     x = jnp.zeros((), dtype=dtype)
     out = fn(x)