修改路径层级

README.md

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+#梅阳阳的学习空间
+
+###分享源码阅读相关笔记

笔记/BERT.md

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+#待定

笔记/CNN-Transformer.md

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+1.位置向量
+```python
+class PositionEmbeddingSine(nn.Module):
+    """
+    This is a more standard version of the position embedding, very similar to the one
+    used by the Attention is all you need paper, generalized to work on images.
+    """
+    def __init__(self, num_pos_feats=64, temperature=10000, normalize=False, scale=None):
+        super().__init__()
+        self.num_pos_feats = num_pos_feats
+        self.temperature = temperature
+        self.normalize = normalize
+        if scale is not None and normalize is False:
+            raise ValueError("normalize should be True if scale is passed")
+        if scale is None:
+            scale = 2 * math.pi
+        self.scale = scale
+
+    def forward(self, tensor_list: NestedTensor):
+        x = tensor_list.tensors
+        mask = tensor_list.mask
+        assert mask is not None
+        not_mask = ~mask
+        y_embed = not_mask.cumsum(1, dtype=torch.float32)
+        x_embed = not_mask.cumsum(2, dtype=torch.float32)
+        if self.normalize:
+            eps = 1e-6
+            y_embed = y_embed / (y_embed[:, -1:, :] + eps) * self.scale
+            x_embed = x_embed / (x_embed[:, :, -1:] + eps) * self.scale
+
+        dim_t = torch.arange(self.num_pos_feats, dtype=torch.float32, device=x.device)
+        dim_t = self.temperature ** (2 * (dim_t // 2) / self.num_pos_feats)
+
+        pos_x = x_embed[:, :, :, None] / dim_t
+        pos_y = y_embed[:, :, :, None] / dim_t
+        pos_x = torch.stack((pos_x[:, :, :, 0::2].sin(), pos_x[:, :, :, 1::2].cos()), dim=4).flatten(3)
+        pos_y = torch.stack((pos_y[:, :, :, 0::2].sin(), pos_y[:, :, :, 1::2].cos()), dim=4).flatten(3)
+        pos = torch.cat((pos_y, pos_x), dim=3).permute(0, 3, 1, 2)
+        return pos
+```
+2.构造resnet提取cnn特征
+```python
+class Backbone(BackboneBase):
+    """ResNet backbone with frozen BatchNorm."""
+    def __init__(self, name: str,
+                 train_backbone: bool,
+                 return_interm_layers: bool,
+                 dilation: bool):
+        backbone = getattr(torchvision.models, name)(
+            replace_stride_with_dilation=[False, False, dilation],
+            pretrained=is_main_process(), norm_layer=FrozenBatchNorm2d)
+        num_channels = 512 if name in ('resnet18', 'resnet34') else 2048
+        super().__init__(backbone, train_backbone, num_channels, return_interm_layers)
+```
+
+3.transformer使用multihead_attention进行第二次编码，然后继续使用multihead_attention进行解码
+
+整体流程如下
+```python
+class Transformer(nn.Module):
+
+    def __init__(self, d_model=512, nhead=8, num_encoder_layers=6,
+                 num_decoder_layers=6, dim_feedforward=2048, dropout=0.1,
+                 activation="relu", normalize_before=False,
+                 return_intermediate_dec=False):
+        super().__init__()
+
+        encoder_layer = TransformerEncoderLayer(d_model, nhead, dim_feedforward,
+                                                dropout, activation, normalize_before)
+        encoder_norm = nn.LayerNorm(d_model) if normalize_before else None
+        self.encoder = TransformerEncoder(encoder_layer, num_encoder_layers, encoder_norm)
+
+        decoder_layer = TransformerDecoderLayer(d_model, nhead, dim_feedforward,
+                                                dropout, activation, normalize_before)
+        decoder_norm = nn.LayerNorm(d_model)
+        self.decoder = TransformerDecoder(decoder_layer, num_decoder_layers, decoder_norm,
+                                          return_intermediate=return_intermediate_dec)
+
+        self._reset_parameters()
+
+        self.d_model = d_model
+        self.nhead = nhead
+
+    def _reset_parameters(self):
+        for p in self.parameters():
+            if p.dim() > 1:
+                nn.init.xavier_uniform_(p)
+
+    def forward(self, src, mask, query_embed, pos_embed):
+        # flatten NxCxHxW to HWxNxC
+        bs, c, h, w = src.shape
+        src = src.flatten(2).permute(2, 0, 1)
+        pos_embed = pos_embed.flatten(2).permute(2, 0, 1)
+        query_embed = query_embed.unsqueeze(1).repeat(1, bs, 1)
+        mask = mask.flatten(1)
+
+        tgt = torch.zeros_like(query_embed)
+        memory = self.encoder(src, src_key_padding_mask=mask, pos=pos_embed)
+        hs = self.decoder(tgt, memory, memory_key_padding_mask=mask,
+                          pos=pos_embed, query_pos=query_embed)
+        return hs.transpose(1, 2), memory.permute(1, 2, 0).view(bs, c, h, w)
+
+```
+
+
+第二次编码过程如下
+```python
+class TransformerEncoderLayer(nn.Module):
+
+    def __init__(self, d_model, nhead, dim_feedforward=2048, dropout=0.1,
+                 activation="relu", normalize_before=False):
+        super().__init__()
+        self.self_attn = nn.MultiheadAttention(d_model, nhead, dropout=dropout)
+        # Implementation of Feedforward model
+        self.linear1 = nn.Linear(d_model, dim_feedforward)
+        self.dropout = nn.Dropout(dropout)
+        self.linear2 = nn.Linear(dim_feedforward, d_model)
+
+        self.norm1 = nn.LayerNorm(d_model)
+        self.norm2 = nn.LayerNorm(d_model)
+        self.dropout1 = nn.Dropout(dropout)
+        self.dropout2 = nn.Dropout(dropout)
+
+        self.activation = _get_activation_fn(activation)
+        self.normalize_before = normalize_before
+
+    def with_pos_embed(self, tensor, pos: Optional[Tensor]):
+        return tensor if pos is None else tensor + pos
+
+    def forward_post(self,
+                     src,
+                     src_mask: Optional[Tensor] = None,
+                     src_key_padding_mask: Optional[Tensor] = None,
+                     pos: Optional[Tensor] = None):
+        q = k = self.with_pos_embed(src, pos)
+        src2 = self.self_attn(q, k, value=src, attn_mask=src_mask,
+                              key_padding_mask=src_key_padding_mask)[0]
+        src = src + self.dropout1(src2)
+        src = self.norm1(src)
+        src2 = self.linear2(self.dropout(self.activation(self.linear1(src))))
+        src = src + self.dropout2(src2)
+        src = self.norm2(src)
+        return src
+
+    def forward_pre(self, src,
+                    src_mask: Optional[Tensor] = None,
+                    src_key_padding_mask: Optional[Tensor] = None,
+                    pos: Optional[Tensor] = None):
+        src2 = self.norm1(src)
+        q = k = self.with_pos_embed(src2, pos)
+        src2 = self.self_attn(q, k, value=src2, attn_mask=src_mask,
+                              key_padding_mask=src_key_padding_mask)[0]
+        src = src + self.dropout1(src2)
+        src2 = self.norm2(src)
+        src2 = self.linear2(self.dropout(self.activation(self.linear1(src2))))
+        src = src + self.dropout2(src2)
+        return src
+
+    def forward(self, src,
+                src_mask: Optional[Tensor] = None,
+                src_key_padding_mask: Optional[Tensor] = None,
+                pos: Optional[Tensor] = None):
+        if self.normalize_before:
+            return self.forward_pre(src, src_mask, src_key_padding_mask, pos)
+        return self.forward_post(src, src_mask, src_key_padding_mask, pos)
+```
+
+```python
+class TransformerEncoder(nn.Module):
+
+    def __init__(self, encoder_layer, num_layers, norm=None):
+        super().__init__()
+        self.layers = _get_clones(encoder_layer, num_layers)
+        self.num_layers = num_layers
+        self.norm = norm
+
+    def forward(self, src,
+                mask: Optional[Tensor] = None,
+                src_key_padding_mask: Optional[Tensor] = None,
+                pos: Optional[Tensor] = None):
+        output = src
+
+        for layer in self.layers:
+            output = layer(output, src_mask=mask,
+                           src_key_padding_mask=src_key_padding_mask, pos=pos)
+
+        if self.norm is not None:
+            output = self.norm(output)
+
+        return output
+```
+
+
+编码细节
+```python
+q = k = self.with_pos_embed(src2, pos)
+src2 = self.self_attn(q, k, value=src2, attn_mask=src_mask,
+                      key_padding_mask=src_key_padding_mask)[0]
+```
+
+
+解码过程如下
+```python
+class TransformerDecoderLayer(nn.Module):
+
+    def __init__(self, d_model, nhead, dim_feedforward=2048, dropout=0.1,
+                 activation="relu", normalize_before=False):
+        super().__init__()
+        self.self_attn = nn.MultiheadAttention(d_model, nhead, dropout=dropout)
+        self.multihead_attn = nn.MultiheadAttention(d_model, nhead, dropout=dropout)
+        # Implementation of Feedforward model
+        self.linear1 = nn.Linear(d_model, dim_feedforward)
+        self.dropout = nn.Dropout(dropout)
+        self.linear2 = nn.Linear(dim_feedforward, d_model)
+
+        self.norm1 = nn.LayerNorm(d_model)
+        self.norm2 = nn.LayerNorm(d_model)
+        self.norm3 = nn.LayerNorm(d_model)
+        self.dropout1 = nn.Dropout(dropout)
+        self.dropout2 = nn.Dropout(dropout)
+        self.dropout3 = nn.Dropout(dropout)
+
+        self.activation = _get_activation_fn(activation)
+        self.normalize_before = normalize_before
+
+    def with_pos_embed(self, tensor, pos: Optional[Tensor]):
+        return tensor if pos is None else tensor + pos
+
+    def forward_post(self, tgt, memory,
+                     tgt_mask: Optional[Tensor] = None,
+                     memory_mask: Optional[Tensor] = None,
+                     tgt_key_padding_mask: Optional[Tensor] = None,
+                     memory_key_padding_mask: Optional[Tensor] = None,
+                     pos: Optional[Tensor] = None,
+                     query_pos: Optional[Tensor] = None):
+        q = k = self.with_pos_embed(tgt, query_pos)
+        tgt2 = self.self_attn(q, k, value=tgt, attn_mask=tgt_mask,
+                              key_padding_mask=tgt_key_padding_mask)[0]
+        tgt = tgt + self.dropout1(tgt2)
+        tgt = self.norm1(tgt)
+        tgt2 = self.multihead_attn(query=self.with_pos_embed(tgt, query_pos),
+                                   key=self.with_pos_embed(memory, pos),
+                                   value=memory, attn_mask=memory_mask,
+                                   key_padding_mask=memory_key_padding_mask)[0]
+        tgt = tgt + self.dropout2(tgt2)
+        tgt = self.norm2(tgt)
+        tgt2 = self.linear2(self.dropout(self.activation(self.linear1(tgt))))
+        tgt = tgt + self.dropout3(tgt2)
+        tgt = self.norm3(tgt)
+        return tgt
+
+    def forward_pre(self, tgt, memory,
+                    tgt_mask: Optional[Tensor] = None,
+                    memory_mask: Optional[Tensor] = None,
+                    tgt_key_padding_mask: Optional[Tensor] = None,
+                    memory_key_padding_mask: Optional[Tensor] = None,
+                    pos: Optional[Tensor] = None,
+                    query_pos: Optional[Tensor] = None):
+        tgt2 = self.norm1(tgt)
+        q = k = self.with_pos_embed(tgt2, query_pos)
+        tgt2 = self.self_attn(q, k, value=tgt2, attn_mask=tgt_mask,
+                              key_padding_mask=tgt_key_padding_mask)[0]
+        tgt = tgt + self.dropout1(tgt2)
+        tgt2 = self.norm2(tgt)
+        tgt2 = self.multihead_attn(query=self.with_pos_embed(tgt2, query_pos),
+                                   key=self.with_pos_embed(memory, pos),
+                                   value=memory, attn_mask=memory_mask,
+                                   key_padding_mask=memory_key_padding_mask)[0]
+        tgt = tgt + self.dropout2(tgt2)
+        tgt2 = self.norm3(tgt)
+        tgt2 = self.linear2(self.dropout(self.activation(self.linear1(tgt2))))
+        tgt = tgt + self.dropout3(tgt2)
+        return tgt
+
+    def forward(self, tgt, memory,
+                tgt_mask: Optional[Tensor] = None,
+                memory_mask: Optional[Tensor] = None,
+                tgt_key_padding_mask: Optional[Tensor] = None,
+                memory_key_padding_mask: Optional[Tensor] = None,
+                pos: Optional[Tensor] = None,
+                query_pos: Optional[Tensor] = None):
+        if self.normalize_before:
+            return self.forward_pre(tgt, memory, tgt_mask, memory_mask,
+                                    tgt_key_padding_mask, memory_key_padding_mask, pos, query_pos)
+        return self.forward_post(tgt, memory, tgt_mask, memory_mask,
+                                 tgt_key_padding_mask, memory_key_padding_mask, pos, query_pos)
+
+```
+
+```python
+class TransformerDecoder(nn.Module):
+
+    def __init__(self, decoder_layer, num_layers, norm=None, return_intermediate=False):
+        super().__init__()
+        self.layers = _get_clones(decoder_layer, num_layers)
+        self.num_layers = num_layers
+        self.norm = norm
+        self.return_intermediate = return_intermediate
+
+    def forward(self, tgt, memory,
+                tgt_mask: Optional[Tensor] = None,
+                memory_mask: Optional[Tensor] = None,
+                tgt_key_padding_mask: Optional[Tensor] = None,
+                memory_key_padding_mask: Optional[Tensor] = None,
+                pos: Optional[Tensor] = None,
+                query_pos: Optional[Tensor] = None):
+        output = tgt
+
+        intermediate = []
+
+        for layer in self.layers:
+            output = layer(output, memory, tgt_mask=tgt_mask,
+                           memory_mask=memory_mask,
+                           tgt_key_padding_mask=tgt_key_padding_mask,
+                           memory_key_padding_mask=memory_key_padding_mask,
+                           pos=pos, query_pos=query_pos)
+            if self.return_intermediate:
+                intermediate.append(self.norm(output))
+
+        if self.norm is not None:
+            output = self.norm(output)
+            if self.return_intermediate:
+                intermediate.pop()
+                intermediate.append(output)
+
+        if self.return_intermediate:
+            return torch.stack(intermediate)
+
+        return output.unsqueeze(0)
+```
+
+
+
+4.前向计算
+```python
+class DETR(nn.Module):
+    """ This is the DETR module that performs object detection """
+    def __init__(self, backbone, transformer, num_classes, num_queries, aux_loss=False):
+        """ Initializes the model.
+        Parameters:
+            backbone: torch module of the backbone to be used. See backbone.py
+            transformer: torch module of the transformer architecture. See transformer.py
+            num_classes: number of object classes
+            num_queries: number of object queries, ie detection slot. This is the maximal number of objects
+                         DETR can detect in a single image. For COCO, we recommend 100 queries.
+            aux_loss: True if auxiliary decoding losses (loss at each decoder layer) are to be used.
+        """
+        super().__init__()
+        self.num_queries = num_queries
+        self.transformer = transformer
+        hidden_dim = transformer.d_model
+        self.class_embed = nn.Linear(hidden_dim, num_classes + 1)
+        self.bbox_embed = MLP(hidden_dim, hidden_dim, 4, 3)
+        self.query_embed = nn.Embedding(num_queries, hidden_dim)
+        self.input_proj = nn.Conv2d(backbone.num_channels, hidden_dim, kernel_size=1)
+        self.backbone = backbone
+        self.aux_loss = aux_loss
+
+    def forward(self, samples: NestedTensor):
+        """ The forward expects a NestedTensor, which consists of:
+               - samples.tensor: batched images, of shape [batch_size x 3 x H x W]
+               - samples.mask: a binary mask of shape [batch_size x H x W], containing 1 on padded pixels
+
+            It returns a dict with the following elements:
+               - "pred_logits": the classification logits (including no-object) for all queries.
+                                Shape= [batch_size x num_queries x (num_classes + 1)]
+               - "pred_boxes": The normalized boxes coordinates for all queries, represented as
+                               (center_x, center_y, height, width). These values are normalized in [0, 1],
+                               relative to the size of each individual image (disregarding possible padding).
+                               See PostProcess for information on how to retrieve the unnormalized bounding box.
+               - "aux_outputs": Optional, only returned when auxilary losses are activated. It is a list of
+                                dictionnaries containing the two above keys for each decoder layer.
+        """
+        if isinstance(samples, (list, torch.Tensor)):
+            samples = nested_tensor_from_tensor_list(samples)
+        features, pos = self.backbone(samples)
+
+        src, mask = features[-1].decompose()
+        assert mask is not None
+        hs = self.transformer(self.input_proj(src), mask, self.query_embed.weight, pos[-1])[0]
+
+        outputs_class = self.class_embed(hs)
+        outputs_coord = self.bbox_embed(hs).sigmoid()
+        out = {'pred_logits': outputs_class[-1], 'pred_boxes': outputs_coord[-1]}
+        if self.aux_loss:
+            out['aux_outputs'] = self._set_aux_loss(outputs_class, outputs_coord)
+        return out
+
+    @torch.jit.unused
+    def _set_aux_loss(self, outputs_class, outputs_coord):
+        # this is a workaround to make torchscript happy, as torchscript
+        # doesn't support dictionary with non-homogeneous values, such
+        # as a dict having both a Tensor and a list.
+        return [{'pred_logits': a, 'pred_boxes': b}
+                for a, b in zip(outputs_class[:-1], outputs_coord[:-1])]
+```
+
+5.计算损失
+首先把hs转化为 目标的类别
+```
+self.class_embed = nn.Linear(hidden_dim, num_classes + 1)
+self.bbox_embed = MLP(hidden_dim, hidden_dim, 4, 3)
+
+class MLP(nn.Module):
+    """ Very simple multi-layer perceptron (also called FFN)"""
+
+    def __init__(self, input_dim, hidden_dim, output_dim, num_layers):
+        super().__init__()
+        self.num_layers = num_layers
+        h = [hidden_dim] * (num_layers - 1)
+        self.layers = nn.ModuleList(nn.Linear(n, k) for n, k in zip([input_dim] + h, h + [output_dim]))
+
+    def forward(self, x):
+        for i, layer in enumerate(self.layers):
+            x = F.relu(layer(x)) if i < self.num_layers - 1 else layer(x)
+        return x
+```
+  
+
+```python
+class HungarianMatcher(nn.Module):
+    """This class computes an assignment between the targets and the predictions of the network
+
+    For efficiency reasons, the targets don't include the no_object. Because of this, in general,
+    there are more predictions than targets. In this case, we do a 1-to-1 matching of the best predictions,
+    while the others are un-matched (and thus treated as non-objects).
+    """
+
+    def __init__(self, cost_class: float = 1, cost_bbox: float = 1, cost_giou: float = 1):
+        """Creates the matcher
+
+        Params:
+            cost_class: This is the relative weight of the classification error in the matching cost
+            cost_bbox: This is the relative weight of the L1 error of the bounding box coordinates in the matching cost
+            cost_giou: This is the relative weight of the giou loss of the bounding box in the matching cost
+        """
+        super().__init__()
+        self.cost_class = cost_class
+        self.cost_bbox = cost_bbox
+        self.cost_giou = cost_giou
+        assert cost_class != 0 or cost_bbox != 0 or cost_giou != 0, "all costs cant be 0"
+
+    @torch.no_grad()
+    def forward(self, outputs, targets):
+        """ Performs the matching
+
+        Params:
+            outputs: This is a dict that contains at least these entries:
+                 "pred_logits": Tensor of dim [batch_size, num_queries, num_classes] with the classification logits
+                 "pred_boxes": Tensor of dim [batch_size, num_queries, 4] with the predicted box coordinates
+
+            targets: This is a list of targets (len(targets) = batch_size), where each target is a dict containing:
+                 "labels": Tensor of dim [num_target_boxes] (where num_target_boxes is the number of ground-truth
+                           objects in the target) containing the class labels
+                 "boxes": Tensor of dim [num_target_boxes, 4] containing the target box coordinates
+
+        Returns:
+            A list of size batch_size, containing tuples of (index_i, index_j) where:
+                - index_i is the indices of the selected predictions (in order)
+                - index_j is the indices of the corresponding selected targets (in order)
+            For each batch element, it holds:
+                len(index_i) = len(index_j) = min(num_queries, num_target_boxes)
+        """
+        bs, num_queries = outputs["pred_logits"].shape[:2]
+
+        # We flatten to compute the cost matrices in a batch
+        out_prob = outputs["pred_logits"].flatten(0, 1).softmax(-1)  # [batch_size * num_queries, num_classes]
+        out_bbox = outputs["pred_boxes"].flatten(0, 1)  # [batch_size * num_queries, 4]
+
+        # Also concat the target labels and boxes
+        tgt_ids = torch.cat([v["labels"] for v in targets])
+        tgt_bbox = torch.cat([v["boxes"] for v in targets])
+
+        # Compute the classification cost. Contrary to the loss, we don't use the NLL,
+        # but approximate it in 1 - proba[target class].
+        # The 1 is a constant that doesn't change the matching, it can be ommitted.
+        cost_class = -out_prob[:, tgt_ids]
+
+        # Compute the L1 cost between boxes
+        cost_bbox = torch.cdist(out_bbox, tgt_bbox, p=1)
+
+        # Compute the giou cost betwen boxes
+        cost_giou = -generalized_box_iou(box_cxcywh_to_xyxy(out_bbox), box_cxcywh_to_xyxy(tgt_bbox))
+
+        # Final cost matrix
+        C = self.cost_bbox * cost_bbox + self.cost_class * cost_class + self.cost_giou * cost_giou
+        C = C.view(bs, num_queries, -1).cpu()
+
+        sizes = [len(v["boxes"]) for v in targets]
+        indices = [linear_sum_assignment(c[i]) for i, c in enumerate(C.split(sizes, -1))]
+        return [(torch.as_tensor(i, dtype=torch.int64), torch.as_tensor(j, dtype=torch.int64)) for i, j in indices]
+```
+
+