• 經(jīng)典transformer的學(xué)習(xí)

• 文章轉(zhuǎn)自微信公眾號(hào)【機(jī)器學(xué)習(xí)煉丹術(shù)】

• 作者：陳亦新（已授權(quán)）

• 聯(lián)系方式: 微信cyx645016617

• 歡迎交流，共同進(jìn)步

• 代碼細(xì)講

  • transformer

  • Embedding

  • Encoder_MultipleLayers

  • Encoder

• 完整代碼

---

代碼細(xì)講

transformer

class?transformer(nn.Sequential):def?__init__(self,?encoding,?**config):super(transformer,?self).__init__()if?encoding?==?'drug':self.emb?=?Embeddings(config['input_dim_drug'],?config['transformer_emb_size_drug'],?50,?config['transformer_dropout_rate'])self.encoder?=?Encoder_MultipleLayers(config['transformer_n_layer_drug'],?config['transformer_emb_size_drug'],?config['transformer_intermediate_size_drug'],?config['transformer_num_attention_heads_drug'],config['transformer_attention_probs_dropout'],config['transformer_hidden_dropout_rate'])elif?encoding?==?'protein':self.emb?=?Embeddings(config['input_dim_protein'],?config['transformer_emb_size_target'],?545,?config['transformer_dropout_rate'])self.encoder?=?Encoder_MultipleLayers(config['transformer_n_layer_target'],?config['transformer_emb_size_target'],?config['transformer_intermediate_size_target'],?config['transformer_num_attention_heads_target'],config['transformer_attention_probs_dropout'],config['transformer_hidden_dropout_rate'])###?parameter?v?(tuple?of?length?2)?is?from?utils.drug2emb_encoder?def?forward(self,?v):e?=?v[0].long().to(device)e_mask?=?v[1].long().to(device)print(e.shape,e_mask.shape)ex_e_mask?=?e_mask.unsqueeze(1).unsqueeze(2)ex_e_mask?=?(1.0?-?ex_e_mask)?*?-10000.0emb?=?self.emb(e)encoded_layers?=?self.encoder(emb.float(),?ex_e_mask.float())return?encoded_layers[:,0]

• 只要有兩個(gè)組件，一個(gè)是Embedding層，一個(gè)是Encoder_MultipleLayers模塊；

• forward的輸入v是一個(gè)元組，包含兩個(gè)元素：第一個(gè)是數(shù)據(jù)，第二個(gè)是mask。對(duì)應(yīng)有效數(shù)據(jù)的位置。

Embedding

class?Embeddings(nn.Module):"""Construct?the?embeddings?from?protein/target,?position?embeddings."""def?__init__(self,?vocab_size,?hidden_size,?max_position_size,?dropout_rate):super(Embeddings,?self).__init__()self.word_embeddings?=?nn.Embedding(vocab_size,?hidden_size)self.position_embeddings?=?nn.Embedding(max_position_size,?hidden_size)self.LayerNorm?=?nn.LayerNorm(hidden_size)self.dropout?=?nn.Dropout(dropout_rate)def?forward(self,?input_ids):seq_length?=?input_ids.size(1)position_ids?=?torch.arange(seq_length,?dtype=torch.long,?device=input_ids.device)position_ids?=?position_ids.unsqueeze(0).expand_as(input_ids)words_embeddings?=?self.word_embeddings(input_ids)position_embeddings?=?self.position_embeddings(position_ids)embeddings?=?words_embeddings?+?position_embeddingsembeddings?=?self.LayerNorm(embeddings)embeddings?=?self.dropout(embeddings)return?embeddings

• 包含三個(gè)組件，一個(gè)是Embedding，其他是LayerNorm和Dropout層。

torch.nn.Embedding(num_embeddings,?embedding_dim,?padding_idx=None,max_norm=None,??norm_type=2.0,???scale_grad_by_freq=False,?sparse=False,??_weight=None)

其為一個(gè)簡(jiǎn)單的存儲(chǔ)固定大小的詞典的嵌入向量的查找表，意思就是說(shuō)，給一個(gè)編號(hào)，嵌入層就能返回這個(gè)編號(hào)對(duì)應(yīng)的嵌入向量，嵌入向量反映了各個(gè)編號(hào)代表的符號(hào)之間的語(yǔ)義關(guān)系。

輸入為一個(gè)編號(hào)列表，輸出為對(duì)應(yīng)的符號(hào)嵌入向量列表。

• num_embeddings (python:int) – 詞典的大小尺寸，比如總共出現(xiàn)5000個(gè)詞，那就輸入5000。此時(shí)index為（0-4999）

• embedding_dim (python:int) – 嵌入向量的維度，即用多少維來(lái)表示一個(gè)符號(hào)。

• padding_idx (python:int, optional) – 填充id，比如，輸入長(zhǎng)度為100，但是每次的句子長(zhǎng)度并不一樣，后面就需要用統(tǒng)一的數(shù)字填充，而這里就是指定這個(gè)數(shù)字，這樣，網(wǎng)絡(luò)在遇到填充id時(shí)，就不會(huì)計(jì)算其與其它符號(hào)的相關(guān)性。（初始化為0）

• max_norm (python:float, optional) – 最大范數(shù)，如果嵌入向量的范數(shù)超過(guò)了這個(gè)界限，就要進(jìn)行再歸一化。

• norm_type (python:float, optional) – 指定利用什么范數(shù)計(jì)算，并用于對(duì)比max_norm，默認(rèn)為2范數(shù)。

• scale_grad_by_freq (boolean, optional) – 根據(jù)單詞在mini-batch中出現(xiàn)的頻率，對(duì)梯度進(jìn)行放縮。默認(rèn)為False.

• sparse (bool, optional) – 若為True,則與權(quán)重矩陣相關(guān)的梯度轉(zhuǎn)變?yōu)橄∈鑿埩俊?/p>

舉一個(gè)例子：

如果你的整數(shù)最大超過(guò)了設(shè)置的字典的容量，那么就會(huì)出錯(cuò)誤：

• Embedding其中有可學(xué)習(xí)參數(shù)！是一個(gè)num_embedding * embedding_dim的矩陣。

Encoder_MultipleLayers

class?Encoder_MultipleLayers(nn.Module):def?__init__(self,?n_layer,?hidden_size,?intermediate_size,?num_attention_heads,?attention_probs_dropout_prob,?hidden_dropout_prob):super(Encoder_MultipleLayers,?self).__init__()layer?=?Encoder(hidden_size,?intermediate_size,?num_attention_heads,?attention_probs_dropout_prob,?hidden_dropout_prob)self.layer?=?nn.ModuleList([copy.deepcopy(layer)?for?_?in?range(n_layer)])????def?forward(self,?hidden_states,?attention_mask,?output_all_encoded_layers=True):all_encoder_layers?=?[]for?layer_module?in?self.layer:hidden_states?=?layer_module(hidden_states,?attention_mask)return?hidden_states

• transformer中的embedding，目的是將數(shù)據(jù)轉(zhuǎn)換成對(duì)應(yīng)的向量。這個(gè)Encoder-multilayer則是提取特征的關(guān)鍵。

• 結(jié)構(gòu)很簡(jiǎn)單，就是由==n_layer==個(gè)Encoder堆疊而成。

Encoder

class?Encoder(nn.Module):def?__init__(self,?hidden_size,?intermediate_size,?num_attention_heads,?attention_probs_dropout_prob,?hidden_dropout_prob):super(Encoder,?self).__init__()self.attention?=?Attention(hidden_size,?num_attention_heads,?attention_probs_dropout_prob,?hidden_dropout_prob)self.intermediate?=?Intermediate(hidden_size,?intermediate_size)self.output?=?Output(intermediate_size,?hidden_size,?hidden_dropout_prob)def?forward(self,?hidden_states,?attention_mask):attention_output?=?self.attention(hidden_states,?attention_mask)intermediate_output?=?self.intermediate(attention_output)layer_output?=?self.output(intermediate_output,?attention_output)return?layer_output

• 其中包含了Attention部分，Intermediate和Output。

class?Attention(nn.Module):def?__init__(self,?hidden_size,?num_attention_heads,?attention_probs_dropout_prob,?hidden_dropout_prob):super(Attention,?self).__init__()self.self?=?SelfAttention(hidden_size,?num_attention_heads,?attention_probs_dropout_prob)self.output?=?SelfOutput(hidden_size,?hidden_dropout_prob)def?forward(self,?input_tensor,?attention_mask):self_output?=?self.self(input_tensor,?attention_mask)attention_output?=?self.output(self_output,?input_tensor)return?attention_outputclass?SelfAttention(nn.Module):def?__init__(self,?hidden_size,?num_attention_heads,?attention_probs_dropout_prob):super(SelfAttention,?self).__init__()if?hidden_size?%?num_attention_heads?!=?0:raise?ValueError("The?hidden?size?(%d)?is?not?a?multiple?of?the?number?of?attention?""heads?(%d)"?%?(hidden_size,?num_attention_heads))self.num_attention_heads?=?num_attention_headsself.attention_head_size?=?int(hidden_size?/?num_attention_heads)self.all_head_size?=?self.num_attention_heads?*?self.attention_head_sizeself.query?=?nn.Linear(hidden_size,?self.all_head_size)self.key?=?nn.Linear(hidden_size,?self.all_head_size)self.value?=?nn.Linear(hidden_size,?self.all_head_size)self.dropout?=?nn.Dropout(attention_probs_dropout_prob)def?transpose_for_scores(self,?x):#?num_attention_heads?=?8,?attention_head_size?=?128?/?8?=?16new_x_shape?=?x.size()[:-1]?+?(self.num_attention_heads,?self.attention_head_size)x?=?x.view(*new_x_shape)return?x.permute(0,?2,?1,?3)def?forward(self,?hidden_states,?attention_mask):#?hidden_states.shape?=?[batch,50,128]mixed_query_layer?=?self.query(hidden_states)mixed_key_layer?=?self.key(hidden_states)mixed_value_layer?=?self.value(hidden_states)query_layer?=?self.transpose_for_scores(mixed_query_layer)key_layer?=?self.transpose_for_scores(mixed_key_layer)value_layer?=?self.transpose_for_scores(mixed_value_layer)#?query_layer.shape?=?[batch,8,50,16]#?Take?the?dot?product?between?"query"?and?"key"?to?get?the?raw?attention?scores.attention_scores?=?torch.matmul(query_layer,?key_layer.transpose(-1,?-2))#?attention_score.shape?=?[batch,8,50,50]attention_scores?=?attention_scores?/?math.sqrt(self.attention_head_size)attention_scores?=?attention_scores?+?attention_mask#?Normalize?the?attention?scores?to?probabilities.attention_probs?=?nn.Softmax(dim=-1)(attention_scores)#?This?is?actually?dropping?out?entire?tokens?to?attend?to,?which?might#?seem?a?bit?unusual,?but?is?taken?from?the?original?Transformer?paper.attention_probs?=?self.dropout(attention_probs)context_layer?=?torch.matmul(attention_probs,?value_layer)context_layer?=?context_layer.permute(0,?2,?1,?3).contiguous()new_context_layer_shape?=?context_layer.size()[:-2]?+?(self.all_head_size,)context_layer?=?context_layer.view(*new_context_layer_shape)return?context_layer

這一段和一般的vit處理的流程類似。雖然transformer是從NLP到CV的，但從CV的vit再回看NLP的transformer也是有一種樂(lè)趣。里面要注意的點(diǎn)是multihead的概念。本來(lái)hidden-size是128，如果設(shè)置multihead的數(shù)量為8，那么其實(shí)好比卷積里面的通道數(shù)量。會(huì)把128的token看成8個(gè)16個(gè)token，然后分別做自注意力。但是把multihead比作卷積的概念感覺(jué)說(shuō)的過(guò)去，比作分組卷積的概念好像也OK：

• 比作卷積。如果固定了每一個(gè)head的size數(shù)量為16，那么head就好比通道數(shù)，那么增加head的數(shù)量，其實(shí)就是增加了卷積核通道數(shù)的感覺(jué)；

• 比作分組卷積。如果固定了hidden-size的數(shù)量為128，那么head的數(shù)量就是分組的數(shù)量，那么增加head的數(shù)量就好比卷積分組變多，降低了計(jì)算量。

-其他部分的代碼都是FC + LayerNorm +Dropout，不再贅述。

完整代碼

import?torch.nn?as?nn import?torch.nn.functional?as?F import?copy,math class?Embeddings(nn.Module):"""Construct?the?embeddings?from?protein/target,?position?embeddings."""def?__init__(self,?vocab_size,?hidden_size,?max_position_size,?dropout_rate):super(Embeddings,?self).__init__()self.word_embeddings?=?nn.Embedding(vocab_size,?hidden_size)self.position_embeddings?=?nn.Embedding(max_position_size,?hidden_size)self.LayerNorm?=?nn.LayerNorm(hidden_size)self.dropout?=?nn.Dropout(dropout_rate)def?forward(self,?input_ids):seq_length?=?input_ids.size(1)position_ids?=?torch.arange(seq_length,?dtype=torch.long,?device=input_ids.device)position_ids?=?position_ids.unsqueeze(0).expand_as(input_ids)words_embeddings?=?self.word_embeddings(input_ids)position_embeddings?=?self.position_embeddings(position_ids)embeddings?=?words_embeddings?+?position_embeddingsembeddings?=?self.LayerNorm(embeddings)embeddings?=?self.dropout(embeddings)return?embeddings class?Encoder_MultipleLayers(nn.Module):def?__init__(self,?n_layer,?hidden_size,?intermediate_size,?num_attention_heads,?attention_probs_dropout_prob,?hidden_dropout_prob):super(Encoder_MultipleLayers,?self).__init__()layer?=?Encoder(hidden_size,?intermediate_size,?num_attention_heads,?attention_probs_dropout_prob,?hidden_dropout_prob)self.layer?=?nn.ModuleList([copy.deepcopy(layer)?for?_?in?range(n_layer)])????def?forward(self,?hidden_states,?attention_mask,?output_all_encoded_layers=True):all_encoder_layers?=?[]for?layer_module?in?self.layer:hidden_states?=?layer_module(hidden_states,?attention_mask)#if?output_all_encoded_layers:#????all_encoder_layers.append(hidden_states)#if?not?output_all_encoded_layers:#????all_encoder_layers.append(hidden_states)return?hidden_states class?Encoder(nn.Module):def?__init__(self,?hidden_size,?intermediate_size,?num_attention_heads,?attention_probs_dropout_prob,?hidden_dropout_prob):super(Encoder,?self).__init__()self.attention?=?Attention(hidden_size,?num_attention_heads,?attention_probs_dropout_prob,?hidden_dropout_prob)self.intermediate?=?Intermediate(hidden_size,?intermediate_size)self.output?=?Output(intermediate_size,?hidden_size,?hidden_dropout_prob)def?forward(self,?hidden_states,?attention_mask):attention_output?=?self.attention(hidden_states,?attention_mask)intermediate_output?=?self.intermediate(attention_output)layer_output?=?self.output(intermediate_output,?attention_output)return?layer_output???? class?Attention(nn.Module):def?__init__(self,?hidden_size,?num_attention_heads,?attention_probs_dropout_prob,?hidden_dropout_prob):super(Attention,?self).__init__()self.self?=?SelfAttention(hidden_size,?num_attention_heads,?attention_probs_dropout_prob)self.output?=?SelfOutput(hidden_size,?hidden_dropout_prob)def?forward(self,?input_tensor,?attention_mask):self_output?=?self.self(input_tensor,?attention_mask)attention_output?=?self.output(self_output,?input_tensor)return?attention_output??class?SelfAttention(nn.Module):def?__init__(self,?hidden_size,?num_attention_heads,?attention_probs_dropout_prob):super(SelfAttention,?self).__init__()if?hidden_size?%?num_attention_heads?!=?0:raise?ValueError("The?hidden?size?(%d)?is?not?a?multiple?of?the?number?of?attention?""heads?(%d)"?%?(hidden_size,?num_attention_heads))self.num_attention_heads?=?num_attention_headsself.attention_head_size?=?int(hidden_size?/?num_attention_heads)self.all_head_size?=?self.num_attention_heads?*?self.attention_head_sizeself.query?=?nn.Linear(hidden_size,?self.all_head_size)self.key?=?nn.Linear(hidden_size,?self.all_head_size)self.value?=?nn.Linear(hidden_size,?self.all_head_size)self.dropout?=?nn.Dropout(attention_probs_dropout_prob)def?transpose_for_scores(self,?x):new_x_shape?=?x.size()[:-1]?+?(self.num_attention_heads,?self.attention_head_size)x?=?x.view(*new_x_shape)return?x.permute(0,?2,?1,?3)def?forward(self,?hidden_states,?attention_mask):mixed_query_layer?=?self.query(hidden_states)mixed_key_layer?=?self.key(hidden_states)mixed_value_layer?=?self.value(hidden_states)query_layer?=?self.transpose_for_scores(mixed_query_layer)key_layer?=?self.transpose_for_scores(mixed_key_layer)value_layer?=?self.transpose_for_scores(mixed_value_layer)#?Take?the?dot?product?between?"query"?and?"key"?to?get?the?raw?attention?scores.attention_scores?=?torch.matmul(query_layer,?key_layer.transpose(-1,?-2))attention_scores?=?attention_scores?/?math.sqrt(self.attention_head_size)attention_scores?=?attention_scores?+?attention_mask#?Normalize?the?attention?scores?to?probabilities.attention_probs?=?nn.Softmax(dim=-1)(attention_scores)#?This?is?actually?dropping?out?entire?tokens?to?attend?to,?which?might#?seem?a?bit?unusual,?but?is?taken?from?the?original?Transformer?paper.attention_probs?=?self.dropout(attention_probs)context_layer?=?torch.matmul(attention_probs,?value_layer)context_layer?=?context_layer.permute(0,?2,?1,?3).contiguous()new_context_layer_shape?=?context_layer.size()[:-2]?+?(self.all_head_size,)context_layer?=?context_layer.view(*new_context_layer_shape)return?context_layerclass?SelfOutput(nn.Module):def?__init__(self,?hidden_size,?hidden_dropout_prob):super(SelfOutput,?self).__init__()self.dense?=?nn.Linear(hidden_size,?hidden_size)self.LayerNorm?=?nn.LayerNorm(hidden_size)self.dropout?=?nn.Dropout(hidden_dropout_prob)def?forward(self,?hidden_states,?input_tensor):hidden_states?=?self.dense(hidden_states)hidden_states?=?self.dropout(hidden_states)hidden_states?=?self.LayerNorm(hidden_states?+?input_tensor)return?hidden_states???class?Intermediate(nn.Module):def?__init__(self,?hidden_size,?intermediate_size):super(Intermediate,?self).__init__()self.dense?=?nn.Linear(hidden_size,?intermediate_size)def?forward(self,?hidden_states):hidden_states?=?self.dense(hidden_states)hidden_states?=?F.relu(hidden_states)return?hidden_statesclass?Output(nn.Module):def?__init__(self,?intermediate_size,?hidden_size,?hidden_dropout_prob):super(Output,?self).__init__()self.dense?=?nn.Linear(intermediate_size,?hidden_size)self.LayerNorm?=?nn.LayerNorm(hidden_size)self.dropout?=?nn.Dropout(hidden_dropout_prob)def?forward(self,?hidden_states,?input_tensor):hidden_states?=?self.dense(hidden_states)hidden_states?=?self.dropout(hidden_states)hidden_states?=?self.LayerNorm(hidden_states?+?input_tensor)return?hidden_states class?transformer(nn.Sequential):def?__init__(self,?encoding,?**config):super(transformer,?self).__init__()if?encoding?==?'drug':self.emb?=?Embeddings(config['input_dim_drug'],?config['transformer_emb_size_drug'],?50,?config['transformer_dropout_rate'])self.encoder?=?Encoder_MultipleLayers(config['transformer_n_layer_drug'],?config['transformer_emb_size_drug'],?config['transformer_intermediate_size_drug'],?config['transformer_num_attention_heads_drug'],config['transformer_attention_probs_dropout'],config['transformer_hidden_dropout_rate'])elif?encoding?==?'protein':self.emb?=?Embeddings(config['input_dim_protein'],?config['transformer_emb_size_target'],?545,?config['transformer_dropout_rate'])self.encoder?=?Encoder_MultipleLayers(config['transformer_n_layer_target'],?config['transformer_emb_size_target'],?config['transformer_intermediate_size_target'],?config['transformer_num_attention_heads_target'],config['transformer_attention_probs_dropout'],config['transformer_hidden_dropout_rate'])###?parameter?v?(tuple?of?length?2)?is?from?utils.drug2emb_encoder?def?forward(self,?v):e?=?v[0].long().to(device)e_mask?=?v[1].long().to(device)print(e.shape,e_mask.shape)ex_e_mask?=?e_mask.unsqueeze(1).unsqueeze(2)ex_e_mask?=?(1.0?-?ex_e_mask)?*?-10000.0emb?=?self.emb(e)encoded_layers?=?self.encoder(emb.float(),?ex_e_mask.float())return?encoded_layers[:,0]往期精彩回顧適合初學(xué)者入門人工智能的路線及資料下載中國(guó)大學(xué)慕課《機(jī)器學(xué)習(xí)》（黃海廣主講）機(jī)器學(xué)習(xí)及深度學(xué)習(xí)筆記等資料打印機(jī)器學(xué)習(xí)在線手冊(cè)深度學(xué)習(xí)筆記專輯《統(tǒng)計(jì)學(xué)習(xí)方法》的代碼復(fù)現(xiàn)專輯 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