Diversity Acquisition Functions

[jaiswalsuraj487]

Implemented Furthest Acquisition and Centroid Acquisition on commit a6e59ff.

Files Added:

1. astra/torch/al/acquisitions/furthest.py: contain implementation of Furthest acquisition
2. astra/torch/al/acquisitions/centroid.py: contain implementation of Centroid acquisition
3. astra/torch/al/strategies/diversity.py: modified this file as per the need
4. tests/torch/acquisitions/test_furthest.py: contains test for furthest acquisition function.
5. tests/torch/acquisitions/test_centroid.py: contains test for centroid acquisition function.

Passes all test cases, including those already existing(commit: a6e59ff).

Explanation:

1. furthest.py: For the furthest acquisition function, we use the furthest_first method of Class distil.active_learning_strategies.core_set.CoreSet link where we pass dummy object strategy as an argument along with labeled_embeddings, unlabeled_embeddings and n. This returns list of indices of n data points that are furthest from all.
2. centroid.py: For the centroid acquisition function: For the Centroid Acquisition function, we pass labeled_embeddings, unlabeled_embeddings , and n as input.

Below lines initializes min_dist as tensor with all values infinity of size [len(n_pool)] when our n_train is 0.

    if labeled_embeddings.shape[0] == 0:
        min_dist = torch.full((unlabeled_embeddings.shape[0],), float("inf"))

Else we find centroid of train data and then pairwise distance between centroid and all pool data.

    else:
        centroid_embedding = torch.mean(labeled_embeddings, dim=0).unsqueeze(0)
        dist_ctr = torch.cdist(unlabeled_embeddings, centroid_embedding, p=2)
        min_dist = torch.min(dist_ctr, dim=1)[0]

We find index of n points from pool data, which has max distance.

    idxs = []
    for i in range(n):
        idx = torch.argmax(min_dist)
        idxs.append(idx.item())
        dist_new_ctr = torch.cdist(unlabeled_embeddings, unlabeled_embeddings[[idx], :])
        min_dist = torch.minimum(min_dist, dist_new_ctr[:, 0])
    return idxs

3. diversity.py: Since the acquisition function implemented in link takes (unlabeled_embeddings, labeled_embeddings, n) as parameters, I did same and modified diversity.py instead of using (features, pool_indices, context_indices) suggested in diversity.py of sustainability-lab/ASTRA
4. and 5. test_furthest.py and test_centroid: Used CIFAR10 to test. Here we want to pass features extractor of model instead of forward pass of model, so I implemented feature extractor as below:

   
   # Define the model
   net = CNN(32, 3, 3, [4, 8], [2, 3], 10).to(device)

def extract_features(net): def feature_extractor(input_tensor):

Initialize features with the input tensor

    features = input_tensor

    # Apply each layer, activation, and max-pooling
    for layer in net.feature_extractor:
        features = layer(features)
        features = net.activation(features)
        features = net.max_pool(features)
    features = net.flatten(features)
    return features

return feature_extractor

Create a feature extractor callable from the network

feature_extractor = extract_features(net)

This feature_extractor gives us features ie. embedding of input.  
```python
# example: this snippet is not included in code
# input shape: (data_dim, height, width, channels)
input = input.permute(0, 3, 1, 2) #input shape: (data_dim, channels, height, width)
features = feature_extractor(input) # shape (data_dim, feature_dim)

We then pass this feature_extractor in strategy.query() which gives best_indices based on furthest or centroid acquisition provided.

# Query the strategy
best_indices = strategy.query(
    feature_extractor, pool_indices, train_indices, n_query_samples=n_query_samples
)

[patel-zeel]

@jaiswalsuraj487 Now that our plan is broadened, let's not use distil library. Use your own implementation. Can you visually show if your acquisition is picking the correct points?

[jaiswalsuraj487]

@patel-zeel I have made the required changes as per the current version of sustainability-lab:main and added sandbox/diveristy_acquisition_demo.ipynb to show a visual of selected data points using corresponding acquisition functions on dummy data.

[jaiswalsuraj487]

@patel-zeel Added AL notebook for diversity acquisitions notebooks/al/diversity_acq_AL.ipynb