Merge pull request #3 from raulpuric/patch-2

Create LARC.py

apex/parallel/LARC.py

+import torch
+from torch import nn
+from torch.autograd import Variable
+from torch.nn.parameter import Parameter
+
+class LARC(object):
+    def __init__(self, optimizer, trust_coefficient=0.02, epsilon=1e-8):
+        self.param_groups = optimizer.param_groups
+        self.optim = optimizer
+        self.trust_coefficient = trust_coefficient
+        self.eps = epsilon
+
+    def __getstate__(self):
+        return self.optim.__getstate__()
+
+    def __setstate__(self, state):
+        self.optim.__setstate__(state)
+
+    def __repr__(self):
+        return self.optim.__repr__()
+
+    def state_dict(self):
+        return self.optim.state_dict()
+
+    def load_state_dict(self, state_dict):
+        self.optim.load_state_dict(state_dict)
+
+    def zero_grad(self):
+        self.optim.zero_grad()
+
+    def add_param_group(self, param_group):
+        self.optim.add_param_group( param_group)
+
+    def step(self):
+        with torch.no_grad():
+            weight_decays = []
+            for group in self.optim.param_groups:
+                # absorb weight decay control from optimizer
+                weight_decay = group['weight_decay'] if 'weight_decay' in group else 0
+                weight_decays.append(weight_decay)
+                group['weight_decay'] = 0
+                for p in group['params']:
+                    if p.grad is None:
+                        continue
+                    param_norm = torch.norm(p.data)
+                    # calculate adaptive lr + weight decay
+                    adaptive_lr = (param_norm + self.eps) / (torch.norm(p.grad.data) + param_norm * weight_decay + self.eps)
+                    p.grad.data += weight_decay * p.data
+                    p.grad.data *= self.trust_coefficient * adaptive_lr
+        self.optim.step()
+        # return weight decay control to optimizer
+        for i, group in enumerate(self.optim.param_groups):
+            group['weight_decay'] = weight_decays[i]