Prototype generic nas model (cont.).

configs/nas-benchmark/algos/weight-sharing.config

@@ -2,7 +2,7 @@
   "scheduler": ["str",   "cos"],
   "LR"       : ["float", "0.025"],
   "eta_min"  : ["float", "0.001"],
-  "epochs"   : ["int",   "250"],
+  "epochs"   : ["int",   "150"],
   "warmup"   : ["int",   "0"],
   "optim"    : ["str",   "SGD"],
   "decay"    : ["float", "0.0005"],

exps/algos-v2/search-cell.py

@@ -2,7 +2,7 @@
 # Copyright (c) Xuanyi Dong [GitHub D-X-Y], 2020 #
 ######################################################################################
 # python ./exps/algos-v2/search-cell.py --dataset cifar10  --data_path $TORCH_HOME/cifar.python --algo darts-v1 --rand_seed 1
-# python ./exps/algos-v2/search-cell.py --dataset cifar100 --data_path $TORCH_HOME/cifar.python --algo darts-v1
+# python ./exps/algos-v2/search-cell.py --dataset cifar100 --data_path $TORCH_HOME/cifar.python --algo darts-v1 --drop_path_rate 0.3
 # python ./exps/algos-v2/search-cell.py --dataset ImageNet16-120 --data_path $TORCH_HOME/cifar.python/ImageNet16 --algo darts-v1
 ####
 # python ./exps/algos-v2/search-cell.py --dataset cifar10  --data_path $TORCH_HOME/cifar.python --algo darts-v2 --rand_seed 1
@@ -30,6 +30,73 @@ from models       import get_cell_based_tiny_net, get_search_spaces
 from nas_201_api  import NASBench201API as API
 
 
+# The following three functions are used for DARTS-V2
+def _concat(xs):
+  return torch.cat([x.view(-1) for x in xs])
+
+
+def _hessian_vector_product(vector, network, criterion, base_inputs, base_targets, r=1e-2):
+  R = r / _concat(vector).norm()
+  for p, v in zip(network.weights, vector):
+    p.data.add_(R, v)
+  _, logits = network(base_inputs)
+  loss = criterion(logits, base_targets)
+  grads_p = torch.autograd.grad(loss, network.alphas)
+
+  for p, v in zip(network.weights, vector):
+    p.data.sub_(2*R, v)
+  _, logits = network(base_inputs)
+  loss = criterion(logits, base_targets)
+  grads_n = torch.autograd.grad(loss, network.alphas)
+
+  for p, v in zip(network.weights, vector):
+    p.data.add_(R, v)
+  return [(x-y).div_(2*R) for x, y in zip(grads_p, grads_n)]
+
+
+def backward_step_unrolled(network, criterion, base_inputs, base_targets, w_optimizer, arch_inputs, arch_targets):
+  # _compute_unrolled_model
+  _, logits = network(base_inputs)
+  loss = criterion(logits, base_targets)
+  LR, WD, momentum = w_optimizer.param_groups[0]['lr'], w_optimizer.param_groups[0]['weight_decay'], w_optimizer.param_groups[0]['momentum']
+  with torch.no_grad():
+    theta = _concat(network.weights)
+    try:
+      moment = _concat(w_optimizer.state[v]['momentum_buffer'] for v in network.weights)
+      moment = moment.mul_(momentum)
+    except:
+      moment = torch.zeros_like(theta)
+    dtheta = _concat(torch.autograd.grad(loss, network.weights)) + WD*theta
+    params = theta.sub(LR, moment+dtheta)
+  unrolled_model = deepcopy(network)
+  model_dict  = unrolled_model.state_dict()
+  new_params, offset = {}, 0
+  for k, v in network.named_parameters():
+    if 'arch_parameters' in k: continue
+    v_length = np.prod(v.size())
+    new_params[k] = params[offset: offset+v_length].view(v.size())
+    offset += v_length
+  model_dict.update(new_params)
+  unrolled_model.load_state_dict(model_dict)
+
+  unrolled_model.zero_grad()
+  _, unrolled_logits = unrolled_model(arch_inputs)
+  unrolled_loss = criterion(unrolled_logits, arch_targets)
+  unrolled_loss.backward()
+
+  dalpha = unrolled_model.arch_parameters.grad
+  vector = [v.grad.data for v in unrolled_model.weights]
+  [implicit_grads] = _hessian_vector_product(vector, network, criterion, base_inputs, base_targets)
+  
+  dalpha.data.sub_(LR, implicit_grads.data)
+
+  if network.arch_parameters.grad is None:
+    network.arch_parameters.grad = deepcopy( dalpha )
+  else:
+    network.arch_parameters.grad.data.copy_( dalpha.data )
+  return unrolled_loss.detach(), unrolled_logits.detach()
+
+
 def search_func(xloader, network, criterion, scheduler, w_optimizer, a_optimizer, epoch_str, print_freq, algo, logger):
   data_time, batch_time = AverageMeter(), AverageMeter()
   base_losses, base_top1, base_top5 = AverageMeter(), AverageMeter(), AverageMeter()
@@ -81,6 +148,9 @@ def search_func(xloader, network, criterion, scheduler, w_optimizer, a_optimizer
     else:
       raise ValueError('Invalid algo name : {:}'.format(algo))
     network.zero_grad()
+    if algo == 'darts-v2':
+      arch_loss, logits = backward_step_unrolled(network, criterion, base_inputs, base_targets, w_optimizer, arch_inputs, arch_targets)
+    else:
       _, logits = network(arch_inputs)
       arch_loss = criterion(logits, arch_targets)
       arch_loss.backward()
@@ -192,7 +262,10 @@ def main(xargs):
   params = count_parameters_in_MB(search_model)
   logger.log('The parameters of the search model = {:.2f} MB'.format(params))
   logger.log('search-space : {:}'.format(search_space))
+  try:
     api = API()
+  except:
+    api = None
   logger.log('{:} create API = {:} done'.format(time_string(), api))
 
   last_info, model_base_path, model_best_path = logger.path('info'), logger.path('model'), logger.path('best')
@@ -224,6 +297,7 @@ def main(xargs):
     epoch_str = '{:03d}-{:03d}'.format(epoch, total_epoch)
     logger.log('\n[Search the {:}-th epoch] {:}, LR={:}'.format(epoch_str, need_time, min(w_scheduler.get_lr())))
 
+    network.set_drop_path(float(epoch+1) / total_epoch, xargs.drop_path_rate)
     search_w_loss, search_w_top1, search_w_top5, search_a_loss, search_a_top1, search_a_top5 \
                 = search_func(search_loader, network, criterion, w_scheduler, w_optimizer, a_optimizer, epoch_str, xargs.print_freq, xargs.algo, logger)
     search_time.update(time.time() - start_time)
@@ -314,6 +388,7 @@ if __name__ == '__main__':
   # architecture leraning rate
   parser.add_argument('--arch_learning_rate', type=float, default=3e-4, help='learning rate for arch encoding')
   parser.add_argument('--arch_weight_decay',  type=float, default=1e-3, help='weight decay for arch encoding')
+  parser.add_argument('--drop_path_rate'  ,  type=float, help='The drop path rate.')
   # log
   parser.add_argument('--workers',            type=int,   default=2,    help='number of data loading workers (default: 2)')
   parser.add_argument('--save_dir',           type=str,   default='./output/search', help='Folder to save checkpoints and log.')

lib/models/cell_searchs/generic_model.py

@@ -67,6 +67,14 @@ class GenericNAS201Model(nn.Module):
     if mode == 'dynamic': self.dynamic_cell = deepcopy(dynamic_cell)
     else                : self.dynamic_cell = None
 
+  def set_drop_path(self, progress, drop_path_rate):
+    if drop_path_rate is None:
+      self._drop_path = None
+    elif progress is None:
+      self._drop_path = drop_path_rate
+    else:
+      self._drop_path = progress * drop_path_rate
+
   @property
   def mode(self):
     return self._mode
@@ -210,6 +218,8 @@ class GenericNAS201Model(nn.Module):
           feature = cell.forward_gdas(feature, alphas, index)
         else: raise ValueError('invalid mode={:}'.format(self.mode))
       else: feature = cell(feature)
+      if self.drop_path is not None:
+        feature = drop_path(feature, self.drop_path)
     out = self.lastact(feature)
     out = self.global_pooling(out)
     out = out.view(out.size(0), -1)