From 09cfcf97e0e938a93867c7d445f1c9b4dcfea023 Mon Sep 17 00:00:00 2001
From: Samuel Fadel <samuelfadel@gmail.com>
Date: Tue, 16 Apr 2019 15:33:58 -0300
Subject: Initial commit.

---
 torch_ema/ema.py | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)
 create mode 100644 torch_ema/ema.py

(limited to 'torch_ema/ema.py')

diff --git a/torch_ema/ema.py b/torch_ema/ema.py
new file mode 100644
index 0000000..32ed7ca
--- /dev/null
+++ b/torch_ema/ema.py
@@ -0,0 +1,59 @@
+from __future__ import division
+from __future__ import unicode_literals
+
+import torch
+
+
+# Partially based on: https://github.com/tensorflow/tensorflow/blob/r1.13/tensorflow/python/training/moving_averages.py
+class ExponentialMovingAverage:
+    """
+    Maintains (exponential) moving average of a set of parameters.
+    """
+    def __init__(self, parameters, decay, use_num_updates=True):
+        """
+        Args:
+          parameters: Iterable of `torch.nn.Parameter`; usually the result of
+            `model.parameters()`.
+          decay: The exponential decay.
+          use_num_updates: Whether to use number of updates when computing
+            averages.
+        """
+        if decay < 0.0 or decay > 1.0:
+            raise ValueError('Decay must be between 0 and 1')
+        self.decay = decay
+        self.num_updates = 0 if use_num_updates else None
+        self.shadow_params = [p.clone().detach()
+                              for p in parameters if p.requires_grad]
+
+    def update(self, parameters):
+        """
+        Update currently maintained parameters.
+
+        Call this every time the parameters are updated, such as the result of
+        the `optimizer.step()` call.
+
+        Args:
+          parameters: Iterable of `torch.nn.Parameter`; usually the same set of
+            parameters used to initialize this object.
+        """
+        decay = self.decay
+        if self.num_updates is not None:
+            self.num_updates += 1
+            decay = min(decay, (1 + self.num_updates) / (10 + self.num_updates))
+        one_minus_decay = 1.0 - decay
+        with torch.no_grad():
+            for s_param, param in zip(self.shadow_params, parameters):
+                if param.requires_grad:
+                    s_param.sub_(one_minus_decay * (s_param - param))
+
+    def copy_to(self, parameters):
+        """
+        Copies current parameters into given collection of parameters.
+
+        Args: 
+          parameters: Iterable of `torch.nn.Parameter`; the parameters to be
+            updated with the stored moving averages.
+        """
+        for s_param, param in zip(self.shadow_params, parameters):
+            if param.requires_grad:
+                param.data.copy_(s_param.data)
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