Activations LeakyReLU / PReLU / Softplus / Mish (#109)

* Leaky_relu / prelu / softplus / mish

* added tests

* updated bench

* remove torch refs, add init to PReLU

* added arvix reference to mish

* added missing docs

benchmarks/python/comparative/bench_mlx.py

@@ -96,7 +96,35 @@ def softmax_fused(axis, x):
 def relu(x):
     y = x
     for i in range(100):
-        y = mx.maximum(y, 0)
+        y = nn.relu(y)
+    mx.eval(y)
+
+
+def leaky_relu(x: mx.array):
+    y = x
+    for i in range(100):
+        y = nn.leaky_relu(y)
+    mx.eval(y)
+
+
+def prelu(x: mx.array):
+    y = x
+    for i in range(100):
+        y = nn.prelu(y, mx.ones(1))
+    mx.eval(y)
+
+
+def softplus(x: mx.array):
+    y = x
+    for i in range(100):
+        y = nn.softplus(y)
+    mx.eval(y)
+
+
+def mish(x: mx.array):
+    y = x
+    for i in range(100):
+        y = nn.mish(y)
     mx.eval(y)
 
 
@@ -334,24 +362,26 @@ if __name__ == "__main__":
     elif args.benchmark == "relu":
         print(bench(relu, x))
 
-    elif args.benchmark == "leaky_relu":
-        print(bench(leaky_relu, x))
-
     elif args.benchmark == "elu":
         print(bench(elu, x))
 
     elif args.benchmark == "relu6":
         print(bench(relu6, x))
 
-    elif args.benchmark == "softplus":
-        print(bench(softplus, x))
-
     elif args.benchmark == "celu":
         print(bench(celu, x))
 
     elif args.benchmark == "log_sigmoid":
         print(bench(log_sigmoid, x))
 
+    elif args.benchmark == "leaky_relu":
+        print(bench(leaky_relu, x))
+    elif args.benchmark == "prelu":
+        print(bench(prelu, x))
+    elif args.benchmark == "softplus":
+        print(bench(softplus, x))
+    elif args.benchmark == "mish":
+        print(bench(mish, x))
     elif args.benchmark == "scalar_mul":
         print(bench(scalar_mult, x))
 

benchmarks/python/comparative/bench_torch.py

@@ -163,6 +163,22 @@ def log_sigmoid(x):
     sync_if_needed(x)
 
 
+@torch.no_grad()
+def prelu(x: torch.Tensor) -> torch.Tensor:
+    y = x
+    for _ in range(100):
+        y = torch.nn.functional.prelu(y, torch.ones(1).to(y.device))
+    sync_if_needed(x)
+
+
+@torch.no_grad()
+def mish(x: torch.Tensor) -> torch.Tensor:
+    y = x
+    for _ in range(100):
+        return torch.nn.functional.mish(y)
+    sync_if_needed(x)
+
+
 @torch.no_grad()
 def scalar_mult(x):
     y = x
@@ -376,6 +392,10 @@ if __name__ == "__main__":
     elif args.benchmark == "log_sigmoid":
         print(bench(log_sigmoid, x))
 
+    elif args.benchmark == "prelu":
+        print(bench(prelu, x))
+    elif args.benchmark == "mish":
+        print(bench(mish, x))
     elif args.benchmark == "scalar_mul":
         print(bench(scalar_mult, x))
 

benchmarks/python/comparative/compare.py

@@ -209,6 +209,11 @@ if __name__ == "__main__":
     compare_filtered("step --size 32x16x1024 --cpu")
     compare_filtered("selu --size 32x16x1024")
     compare_filtered("selu --size 32x16x1024 --cpu")
+    # compare_filtered("mish --size 32x16x1024") NOTE: Torch does not implement Mish in MPS atm
+    compare_filtered("mish --size 32x16x1024 --cpu")
+    compare_filtered("prelu --size 32x16x1024")
+    compare_filtered("prelu --size 32x16x1024 --cpu")
+
     compare_filtered("scalar_mul --size 32x16x1024")
     compare_filtered("scalar_mul --size 32x16x1024 --cpu")
     compare_filtered("cross_entropy --size 256x1024")

docs/src/python/nn.rst

@@ -146,10 +146,12 @@ Neural Network Layers
 
    Embedding
    ReLU
+   PReLU
    GELU
    SiLU
    Step
    SELU
+   Mish
    Linear
    Conv1d
    Conv2d
@@ -171,9 +173,11 @@ simple functions.
    gelu_approx
    gelu_fast_approx
    relu
+   prelu
    silu
    step
    selu
+   mish
 
 Loss Functions
 --------------

python/mlx/nn/layers/__init__.py

@@ -7,6 +7,8 @@ from mlx.nn.layers.activations import (
     SELU,
     LeakyReLU,
     LogSigmoid,
+    Mish,
+    PReLU,
     ReLU,
     ReLU6,
     SiLU,
@@ -19,6 +21,8 @@ from mlx.nn.layers.activations import (
     gelu_fast_approx,
     leaky_relu,
     log_sigmoid,
+    mish,
+    prelu,
     relu,
     relu6,
     selu,

python/mlx/nn/layers/activations.py

@@ -176,6 +176,33 @@ def selu(x):
     See also :func:`elu`.
     """
     return elu(x, 1.67326) * 1.0507
+def prelu(x: mx.array, alpha: mx.array) -> mx.array:
+    r"""Applies the element-wise function:
+
+    .. math::
+        \text{PReLU}(x) = \max(0,x) + a * \min(0,x)
+
+    Here :math:`a` is an array.
+    """
+    return mx.maximum(0, x) + alpha * mx.minimum(0, x)
+
+
+def mish(x: mx.array) -> mx.array:
+    r"""Applies the Mish function, element-wise.
+    Mish: A Self Regularized Non-Monotonic Neural Activation Function.
+
+    Reference: https://arxiv.org/abs/1908.08681
+
+    .. math::
+        \text{Mish}(x) = x * \text{Tanh}(\text{Softplus}(x))
+
+    """
+    return x * mx.tanh(softplus(x))
+
+
+@_make_activation_module(mish)
+class Mish(Module):
+    pass
 
 
 @_make_activation_module(relu)
@@ -257,6 +284,15 @@ class LogSigmoid(Module):
     pass
 
 
+class PReLU(Module):
+    def __init__(self, num_parameters=1, init=0.25):
+        super().__init__()
+        self.weight = mx.full([num_parameters], init)
+
+    def __call__(self, x: mx.array):
+        return prelu(x, self.weight)
+
+
 class GELU(Module):
     r"""Applies the Gaussian Error Linear Units.
 

python/tests/mlx_tests.py

@@ -2,8 +2,10 @@
 
 import os
 import unittest
+from typing import Callable, List, Tuple
 
 import mlx.core as mx
+import numpy as np
 
 
 class MLXTestCase(unittest.TestCase):
@@ -16,3 +18,16 @@ class MLXTestCase(unittest.TestCase):
 
     def tearDown(self):
         mx.set_default_device(self.default)
+
+    def assertEqualArray(
+        self,
+        args: List[mx.array | float | int],
+        mlx_func: Callable[..., mx.array],
+        expected: mx.array,
+        atol=1e-2,
+        rtol=1e-2,
+    ):
+        mx_res = mlx_func(*args)
+        assert tuple(mx_res.shape) == tuple(expected.shape), "shape mismatch"
+        assert mx_res.dtype == expected.dtype, "dtype mismatch"
+        np.testing.assert_allclose(mx_res, expected, rtol=rtol, atol=atol)

python/tests/test_nn.py

@@ -449,31 +449,19 @@ class TestNN(mlx_tests.MLXTestCase):
         self.assertEqual(y.shape, [3])
         self.assertEqual(y.dtype, mx.float32)
 
-    def test_step_activation(self):
-        x = mx.arange(-3, 4)
-        expected = mx.array([0, 0, 0, 0, 0, 1, 1])
-        y = nn.Step()(x)
-        self.assertTrue(mx.array_equal(y, expected))
-
-        y = nn.Step(2)(x)
-        expected = mx.array([0, 0, 0, 0, 0, 0, 1])
-        self.assertTrue(mx.array_equal(y, expected))
-
-    def test_selu(self):
-        x = mx.arange(-3, 4)
-        expected = mx.array(
-            [
-                -1.670563817024231,
-                -1.5201621055603027,
-                -1.1113275289535522,
-                0.0,
-                1.0506999492645264,
-                2.1013998985290527,
-                3.152099847793579,
-            ]
+    def test_prelu(self):
+        self.assertEqualArray(
+            [mx.array([1.0, -1.0, 0.0, 0.5])],
+            nn.PReLU(),
+            mx.array([1.0, -0.25, 0.0, 0.5]),
+        )
+
+    def test_mish(self):
+        self.assertEqualArray(
+            [mx.array([1.0, -1.0, 0.0, 0.5])],
+            nn.Mish(),
+            mx.array([0.8651, -0.3034, 0.0000, 0.3752]),
         )
-        y = nn.SELU()(x)
-        self.assertTrue(mx.allclose(y, expected))
 
 
 if __name__ == "__main__":