added typing hints and fixed some comments

openfold/utils/multi_chain_permutation.py

 import logging
 import random
 import torch
-
+from typing import Tuple, List,Dict
 from openfold.np import residue_constants as rc
 
 logger = logging.getLogger(__name__)
@@ -13,6 +13,17 @@ def compute_rmsd(
     atom_mask: torch.Tensor = None,
     eps: float = 1e-6,
 ) -> torch.Tensor:
+    """
+    Function to calculate RMSD between predicted and ground truth atom position
+
+    Args: 
+        true_atom_pos: a [nres*3] tensor
+        pred_atom_pos: a [nres*3] tensor
+        atom_mask: a [1*nres] tensor
+
+    Return:
+        RMSD value between true and predicted atom positions
+    """
     sq_diff = torch.square(true_atom_pos - pred_atom_pos).sum(dim=-1, keepdim=False)
     if atom_mask is not None:
         sq_diff = torch.masked_select(sq_diff, atom_mask.to(sq_diff.device))
@@ -21,7 +32,7 @@ def compute_rmsd(
     return torch.sqrt(msd + eps)  # prevent sqrt 0
 
 
-def kabsch_rotation(P, Q):
+def kabsch_rotation(P:torch.Tensor, Q:torch.Tensor) -> torch.Tensor:
     """
     Calculate the best rotation that minimises the RMSD between P and Q.
 
@@ -33,7 +44,7 @@ def kabsch_rotation(P, Q):
         Q: [N * 3] the same dimension as P
 
     return:
-    A 3*3 rotation matrix
+        one 3*3 rotation matrix
     """
     assert P.shape == torch.Size([Q.shape[0], Q.shape[1]])
 
@@ -54,8 +65,12 @@ def get_optimal_transform(
     src_atoms: torch.Tensor,
     tgt_atoms: torch.Tensor,
     mask: torch.Tensor = None,
-):
+) -> Tuple[torch.Tensor, torch.Tensor]:
     """
+    A function that obtain the transformation that optimally align 
+    src_atoms with tgt_atoms 
+
+    Args:
         src_atoms: predicted CA positions, shape:[num_res,3]
         tgt_atoms: ground-truth CA positions, shape:[num_res,3]
         mask: a vector of boolean values, shape:[num_res]
@@ -88,7 +103,7 @@ def get_optimal_transform(
     return r, x
 
 
-def get_least_asym_entity_or_longest_length(batch, input_asym_id):
+def get_least_asym_entity_or_longest_length(batch:dict, input_asym_id:list)->Tuple[torch.Tensor, List[torch.Tensor]]:
     """
     First check how many subunit(s) one sequence has. Select the subunit that is less
     common, e.g. if the protein was AABBB then select one of the A as anchor
@@ -145,17 +160,29 @@ def get_least_asym_entity_or_longest_length(batch, input_asym_id):
 
 
 def greedy_align(
-    batch,
-    per_asym_residue_index,
-    entity_2_asym_list,
-    pred_ca_pos,
-    pred_ca_mask,
-    true_ca_poses,
-    true_ca_masks,
-):
+    batch:dict,
+    per_asym_residue_index:dict,
+    entity_2_asym_list:dict,
+    pred_ca_pos:torch.Tensor,
+    pred_ca_mask:torch.Tensor,
+    true_ca_poses:list,
+    true_ca_masks:list
+) -> List[Tuple[int,int]]:
     """
     Implement Algorithm 4 in the Supplementary Information of AlphaFold-Multimer paper:
     Evans,R et al., 2022 Protein complex prediction with AlphaFold-Multimer, bioRxiv 2021.10.04.463034; doi: https://doi.org/10.1101/2021.10.04.463034
+    
+    Args:
+        batch: a dictionary of ground truth features 
+        per_asym_residue_index: a dictionary recording which residues belong to which aysm_id 
+        entity_2_asym_list: a dictionary recording which asym_id(s) belong to which entity_id 
+        pred_ca_pos: predicted positions of c-alpha atoms from the results of model.forward()
+        pred_ca_mask: a boolean tensor that masks pred_ca_pos
+        true_ca_poses: a list of tensors, corresponding to the c-alpha positions of the ground truth structure. e.g. If there are 5 chains, this list will have a length of 5 
+        true_ca_masks: a list of tensors, corresponding to the masks of c-alpha positions of the ground truth structure. If there are 5 chains, this list will have a length of 5 
+    
+    Return:
+        A list of tuple(int,int) that provides instructions of how the ground truth chains should be permuated
     """
     used = [False for _ in range(len(true_ca_poses))]
     align = []
@@ -189,21 +216,38 @@ def greedy_align(
     return align
 
 
-def pad_features(feature_tensor, nres_pad, pad_dim):
-    """Pad input feature tensor"""
+def pad_features(feature_tensor:torch.Tensor, nres_pad:int, pad_dim:int) -> torch.Tensor:
+    """
+    Pad input feature tensor. Padding values will be 0 and put behind the true feature values
+    
+    Args:
+        feature_tensor: A feature tensor 
+        nres_pad: number of residues to add
+        pad_dim: along which dimension of the feature_tensor to pad 
+    
+    Returns:
+        a padded feature tensor
+    """
     pad_shape = list(feature_tensor.shape)
     pad_shape[pad_dim] = nres_pad
     padding_tensor = feature_tensor.new_zeros(pad_shape, device=feature_tensor.device)
     return torch.concat((feature_tensor, padding_tensor), dim=pad_dim)
 
 
-def merge_labels(per_asym_residue_index, labels, align, original_nres):
+def merge_labels(per_asym_residue_index:Dict[int,List[int]], 
+                 labels:dict, align:List[Tuple[int, int]], 
+                 original_nres:int) -> Dict[str,torch.Tensor]:
     """
     Merge ground truth labels according to the permutation results
 
-    labels: list of original ground truth feats
+    Args:
+        per_asym_residue_index: a dictionary recording which residues belong to which aysm_id 
+        labels: list of original ground truth feats e.g. if there're 5 chains, labels will have a length of 5
         align: list of tuples, each entry specify the corresponding label of the asym.
+        original_nres: int, corresponding to the number of residues specified by crop_size in config.py
 
+    Returns:
+        A new dictionary of permuated ground truth features
     modified based on UniFold:
     https://github.com/dptech-corp/Uni-Fold/blob/b1c89a2cebd4e4ee4c47b4e443f92beeb9138fbb/unifold/losses/chain_align.py#L176C1-L176C1
     """
@@ -230,7 +274,7 @@ def merge_labels(per_asym_residue_index, labels, align, original_nres):
     return outs
 
 
-def split_ground_truth_labels(gt_features):
+def split_ground_truth_labels(gt_features:dict) -> List[Dict]:
     """
     Splits ground truth features according to chains
 
@@ -251,7 +295,16 @@ def split_ground_truth_labels(gt_features):
     return labels
 
 
-def get_per_asym_residue_index(features):
+def get_per_asym_residue_index(features: dict) -> Dict[int,list]:
+    """
+    A function that retrieve which residues belong to which asym_id 
+
+    Args:
+        features: a dictionary that contains input features after cropping 
+
+    Returns:
+        A dictionary that records which region of the sequence belongs to which asym_id
+    """
     unique_asym_ids = [i for i in torch.unique(features["asym_id"]) if i != 0]
     per_asym_residue_index = {}
     for cur_asym_id in unique_asym_ids:
@@ -261,7 +314,7 @@ def get_per_asym_residue_index(features):
     return per_asym_residue_index
 
 
-def get_entity_2_asym_list(batch):
+def get_entity_2_asym_list(batch: dict) -> Dict[int,list]:
     """
     Generates a dictionary mapping unique entity IDs to lists of unique asymmetry IDs (asym_id) for each entity.
 
@@ -281,14 +334,16 @@ def get_entity_2_asym_list(batch):
     return entity_2_asym_list
 
 
-def calculate_input_mask(true_ca_masks, anchor_gt_idx, anchor_gt_residue,
-                         asym_mask, pred_ca_mask):
+def calculate_input_mask(true_ca_masks:List[torch.Tensor], anchor_gt_idx:torch.Tensor, 
+                         anchor_gt_residue:list,
+                         asym_mask:torch.Tensor, pred_ca_mask:torch.Tensor) -> torch.Tensor:
     """
     Calculate an input mask for downstream optimal transformation computation
 
     Args:
-        true_ca_masks (Tensor): ca mask from ground truth.
-        anchor_gt_idx (Tensor): The index of selected ground truth anchor.
+        true_ca_masks: list of masks from ground truth chains.
+        anchor_gt_idx (Tensor): a tensor with one integer in it. The index of selected ground truth anchor.
+        anchor_gt_residue:a list of residue indexes that belongs to the selected ground truth anchor
         asym_mask (Tensor): Boolean tensor indicating which regions are selected predicted anchor.
         pred_ca_mask (Tensor): ca mask from predicted structure.
 
@@ -303,11 +358,26 @@ def calculate_input_mask(true_ca_masks, anchor_gt_idx, anchor_gt_residue,
     return input_mask
 
 
-def calculate_optimal_transform(true_ca_poses,
-                                anchor_gt_idx, anchor_gt_residue,
-                                true_ca_masks, pred_ca_mask,
-                                asym_mask,
-                                pred_ca_pos):
+def calculate_optimal_transform(true_ca_poses:List[torch.Tensor],
+                                anchor_gt_idx:int, anchor_gt_residue:list,
+                                true_ca_masks:List[torch.Tensor], pred_ca_mask:torch.Tensor,
+                                asym_mask:torch.Tensor,
+                                pred_ca_pos:torch.Tensor):
+    
+    """
+    Takes selected anchor ground truth c-alpha positions and 
+    selected predicted anchor c-alpha position then calculate the optimal rotation matrix
+    to align ground-truth anchor and predicted anchor
+
+    Args: 
+        true_ca_poses: a list of tensors, corresponding to the c-alpha positions of the ground truth structure. e.g. If there are 5 chains, this list will have a length of 5
+        anchor_gt_idx (Tensor): a tensor with one integer in it. The index of selected ground truth anchor.
+        anchor_gt_residue:a list of residue indexes that belongs to the selected ground truth anchor
+        true_ca_masks: list of masks from ground truth chains e.g. it will be length=5 if there are 5 chains in ground truth structure
+        pred_ca_mask: A boolean tensor corresponds to the mask to mask the predicted features
+        asym_mask: A boolean tensor that mask out other elements in a tensor if they do not belong to a this asym_id
+        pred_ca_pos: a [nres*3] tensor of predicted c-alpha atom positions
+    """
     input_mask = calculate_input_mask(true_ca_masks,
                                       anchor_gt_idx,
                                       anchor_gt_residue,
@@ -326,13 +396,25 @@ def calculate_optimal_transform(true_ca_poses,
     return r, x
 
 
-def compute_permutation_alignment(out, features, ground_truth):
+def compute_permutation_alignment(out:Dict[str,torch.Tensor], 
+                                  features:Dict[str,torch.Tensor], 
+                                  ground_truth:List[Dict[str, torch.Tensor]]) -> Tuple[List[Tuple[int,int]], Dict[int,List[int]]]:
     """
-    A class method that first permutate chains in ground truth first
+    Permutates chains in ground truth first
     before calculating the loss.
 
+    Args:
+        out: a dictionary of output tensors from model.forward()
+        features: a dictionary of feature tensors that are used as input for model.forward()
+        ground_truth: a list of dictionaries of features corresponding to chains in ground truth structure e.g. it will be a length of 5 if  there are 5 chains in ground truth structure
+
+    Returns:
+        best_align: a list of tuple(int,int) that instructs how ground truth chains should be permutated
+        per_asym_residue_index: per_asym_residue_index: a dictionary recording which residues belong to which aysm_id 
     Details are described in Section 7.3 in the Supplementary of AlphaFold-Multimer paper:
     https://www.biorxiv.org/content/10.1101/2021.10.04.463034v2
+
+
     """
     unique_asym_ids = set(torch.unique(features['asym_id']).tolist())
     unique_asym_ids.discard(0)  # Remove padding asym_id
@@ -397,13 +479,19 @@ def compute_permutation_alignment(out, features, ground_truth):
     return best_align, per_asym_residue_index
 
 
-def multi_chain_permutation_align(out, features, ground_truth):
-    """Compute multi-chain permutation alignment.
+def multi_chain_permutation_align(out:Dict[str,torch.Tensor], 
+                                  features:Dict[str,torch.Tensor], 
+                                  ground_truth:List[Dict[str, torch.Tensor]])->Dict[str,torch.Tensor]:
+    """
+    Compute multi-chain permutation alignment.
 
     Args:
-        out: The output of model.forward()
-        features: Input features
-        ground_truth: Ground truth features
+        out: a dictionary of output tensors from model.forward()
+        features: a dictionary of feature tensors that are used as input for model.forward()
+        ground_truth: a list of dictionaries of features corresponding to chains in ground truth structure e.g. it will be a length of 5 if  there are 5 chains in ground truth structure
+    
+    Returns:
+        features: a dictionary with updated ground truth feature tensors, ready for downstream loss calculations.
     """
 
     labels = split_ground_truth_labels(ground_truth)