test-mass-forker-org-1 / ml-data-parameters

Data Parameters: A New Family of Parameters for Learning a Differentiable Curriculum

This repository accompanies the research paper, Data Parameters: A New Family of Parameters for Learning a Differentiable Curriculum (accepted at NeurIPS 2019). The online copy of the poster is available here.

Citation

If you find this code useful in your research then please cite:

@article{saxena2019data,
  title={Data Parameters: A New Family of Parameters for Learning a Differentiable Curriculum},
  author={Saxena, Shreyas and Tuzel, Oncel and DeCoste, Dennis},
  booktitle={NeurIPS},
  year={2019}
}

Data Parameters

In the paper cited above, we have introduced a new family of parameters termed "data parameters". Specifically, we equip each class and training data point with a learnable parameter (data parameters), which governs their importance during different stages of training. Along with the model parameters, the data parameters are also learnt with gradient descent, thereby yielding a curriculum which evolves during the course of training. More importantly, post training, during inference, data parameters are not used, and hence do not alter the model's complexity or run-time at inference.

Setup and Requirements

This code was developed and tested on Nvidia V100 in the following environment.

• Ubuntu 18.04
• Python 3.6.9
• Torch 1.2.0
• Torchvision 0.4

Getting Started

Apart from the system requirements, you would also need to download ImageNet dataset locally. This path needs to be provided to main_imagenet.py with --data argument.

Training model with data parameters

With very little modification, an existing DNN training pipeline can be modified to use data parameters.

• The first modification is change in data loader. In contrast to standard data loaders which return (x_i, y_i) as a tuple. We need to return the index of the sample. This is a one line change in _getitem_ function (see cifar_dataset.py or imagenet_dataset.py). Note, this change is required to implement instance level curriculum. Class level curriculum can be implemented without this modification.

• This brings us to the second change (crucial), change in optimizer. Standard optimizers in a deep learning framework like PyTorch are built for model parameters. They assume that at each iteration, all parameters are involved in the computational graph and receive a gradient. Therefore, at each iteration, all parameters undergo a weight decay penalty, along with an update to their corresponding momentum buffer. These assumptions and updates are valid for model parameters, but not for data parameters. At each iteration, only a subset of data parameters are part of the computational graph (corresponding to classes and instances in the minibatch). Using standard optimizers from PyTorch for data parameters will apply a weight decay penalty on all data parameters at each iteration, and will therefore nullify the learnt curriculum. To circumvent this issue, we apply weight decay explicitly on the subset of data parameters participating in the minibatch. Also, we have implemented a SparseSGD optimizer which performs a sparse update of momentum buffer, updating buffer only for data parameters present in the computational graph. More information can be found in file sparse_sgd.py.

• Apart from these changes, the only change required is instantiation of data parameters and rescaling of logits with data parameters in the forward pass. Since data parameters interact with model at the last layer, in practice, there is negligible overhead in training time.

• The three things which can be tuned for data parameters is their: initialization, learning rate, and weight decay. In practice, we have set initialization of data parameters to 1.0 (initializes training to use standard softmax loss). This leaves us with two hyper-parameters whose value can be set by grid-search. In our experiments, we found data parameters to be robust to variations in these hyper-parameters.

Below we provide example commands along with the hyper-parameters to reproduce results on ImageNet and CIFAR100 noisy dataset from the paper.

ImageNet

Baseline

python main_imagenet.py \
  --arch 'resnet18' \ 
  --gpu 0 \
  --data 'path/to/imagenet' \

This command will train ResNet18 architecture on ImageNet dataset without data parameters. This experiment can be used to obtain baseline performance without data parameters. Running this script, you should obtain 70.2% accuracy on validation @ 100 epoch.

Train with class level parameters

To train ResNet18 with class-level parameters you can use this command:

python main_imagenet.py \
  --arch 'resnet18' \ 
  --data 'path/to/imagenet' \
  --init_class_param 1.0 \
  --lr_class_param 0.1 \
  --wd_class_param 1e-4 \
  --learn_class_paramters \

Note, the learning rate, weight decay and initial value of class parameters can be specified using --lr_class_param, --wd_class_param and --init_class_param respectively. Running this script with the hyper-parameters specified above, you should obtain 70.5% accuracy on validation @ 100 epoch. You can run this script with different values of lr_class_param and wd_class_param to obtain more intuition about data parameters.

To facilitate introspection, the training script dumps the histogram, mean, highest and the lowest value of data parameters in the tensorboard for visualization. For example, in the figure below, we can visualize the histogram of class-level parameters (x-axis) over the course of training (y-axis). The parameters of each class vary in the start of training, but towards the end of training, they all converge to similar value (indicating all classes were given close to equal importance at convergence).

Joint training with class and instance level parameters

As mentioned in the paper, it is possible to train with class and instance level parameters in a joint manner. To train ResNet18 with both parameters you can use this command:

python main_imagenet.py \
  --arch 'resnet18' \ 
  --data 'path/to/imagenet' \
  --init_class_param 1.0 \
  --lr_class_param 0.1 \
  --wd_class_param 1e-4 \
  --init_inst_param 0.001 \
  --lr_inst_param 0.8 \
  --wd_inst_param 1e-8 \
  --learn_class_paramters \
  --learn_inst_parameters 

For joint training setup, class and instance level parameters are initialized to 1.0 and 0.001. This is to ensure that their initial sum is close to 1.0. We did not experiment with other initialization schemes, but data parameters can be initialized with any arbitrary value (greater than 0). Running this script with the hyper-parameters specified above, you should obtain 70.8% accuracy on validation @ 100 epoch.

CIFAR100 Noisy Data

cifar_dataset.py extends the standard CIFAR100 dataset from torchvision to allow corruption of a subset of data with uniform label swap.

Baseline

python main_cifar.py \
  --rand_fraction 0.4 \

This command trains WideResNet28_10 architecture on CIFAR100 dataset (corruption rate=40%) without data parameters. This experiment can be used to obtain baseline performance without data parameters. Running this script, you should obtain 50.0% accuracy at convergence (see Table 2 in paper).

Train with instance level parameters

Since the noise present in the dataset is at instance level, we can train the DNN model with instance level parameters to learn instance specific curriculum. The curriculum should learn to ignore learning from corrupt samples in the dataset.

python main_cifar.py \
  --rand_fraction 0.4 \
  --init_inst_param 1.0 \
  --lr_inst_param 0.2 \
  --wd_inst_param 0.0 \
  --learn_inst_parameters 

Running this script, using instance level parameters, you should obtain 71% accuracy @ 84th epoch. For results on noisy datasets, we always perform early stopping at 84th epoch (set by cross-validation). Running with the same hyper-parameters for instance parameters, for 20% and 80% corruption rate, you should obtain 75% and 35% accuracy respectively.

License

This code is released under the LICENSE terms.