import paddle from paddle import nn import paddle.nn.functional as F from paddle.nn import Linear from paddle.nn.initializer import XavierUniform as xavier_uniform_ from paddle.nn.initializer import Constant as constant_ from paddle.nn.initializer import XavierNormal as xavier_normal_ zeros_ = constant_(value=0.) ones_ = constant_(value=1.) class MultiheadAttentionOptim(nn.Layer): r"""Allows the model to jointly attend to information from different representation subspaces. See reference: Attention Is All You Need .. math:: \text{MultiHead}(Q, K, V) = \text{Concat}(head_1,\dots,head_h)W^O \text{where} head_i = \text{Attention}(QW_i^Q, KW_i^K, VW_i^V) Args: embed_dim: total dimension of the model num_heads: parallel attention layers, or heads Examples:: >>> multihead_attn = nn.MultiheadAttention(embed_dim, num_heads) >>> attn_output, attn_output_weights = multihead_attn(query, key, value) """ def __init__(self, embed_dim, num_heads, dropout=0., bias=True, add_bias_kv=False, add_zero_attn=False): super(MultiheadAttentionOptim, self).__init__() self.embed_dim = embed_dim self.num_heads = num_heads self.dropout = dropout self.head_dim = embed_dim // num_heads assert self.head_dim * num_heads == self.embed_dim, "embed_dim must be divisible by num_heads" self.scaling = self.head_dim ** -0.5 self.out_proj = Linear(embed_dim, embed_dim, bias_attr=bias) self._reset_parameters() self.conv1 = paddle.nn.Conv2D(in_channels=embed_dim, out_channels=embed_dim, kernel_size=(1, 1)) self.conv2 = paddle.nn.Conv2D(in_channels=embed_dim, out_channels=embed_dim, kernel_size=(1, 1)) self.conv3 = paddle.nn.Conv2D(in_channels=embed_dim, out_channels=embed_dim, kernel_size=(1, 1)) def _reset_parameters(self): xavier_uniform_(self.out_proj.weight) def forward(self, query, key, value, key_padding_mask=None, incremental_state=None, need_weights=True, static_kv=False, attn_mask=None): """ Inputs of forward function query: [target length, batch size, embed dim] key: [sequence length, batch size, embed dim] value: [sequence length, batch size, embed dim] key_padding_mask: if True, mask padding based on batch size incremental_state: if provided, previous time steps are cashed need_weights: output attn_output_weights static_kv: key and value are static Outputs of forward function attn_output: [target length, batch size, embed dim] attn_output_weights: [batch size, target length, sequence length] """ tgt_len, bsz, embed_dim = query.shape assert embed_dim == self.embed_dim assert list(query.shape) == [tgt_len, bsz, embed_dim] assert key.shape == value.shape q = self._in_proj_q(query) k = self._in_proj_k(key) v = self._in_proj_v(value) q *= self.scaling q = q.reshape([tgt_len, bsz * self.num_heads, self.head_dim]).transpose([1, 0, 2]) k = k.reshape([-1, bsz * self.num_heads, self.head_dim]).transpose([1, 0, 2]) v = v.reshape([-1, bsz * self.num_heads, self.head_dim]).transpose([1, 0, 2]) src_len = k.shape[1] if key_padding_mask is not None: assert key_padding_mask.shape[0] == bsz assert key_padding_mask.shape[1] == src_len attn_output_weights = paddle.bmm(q, k.transpose([0,2,1])) assert list(attn_output_weights.shape) == [bsz * self.num_heads, tgt_len, src_len] if attn_mask is not None: attn_mask = attn_mask.unsqueeze(0) attn_output_weights += attn_mask if key_padding_mask is not None: attn_output_weights = attn_output_weights.reshape([bsz, self.num_heads, tgt_len, src_len]) key = key_padding_mask.unsqueeze(1).unsqueeze(2).astype('float32') y = paddle.full(shape=key.shape, dtype='float32', fill_value='-inf') y = paddle.where(key==0.,key, y) attn_output_weights += y attn_output_weights = attn_output_weights.reshape([bsz*self.num_heads, tgt_len, src_len]) attn_output_weights = F.softmax( attn_output_weights.astype('float32'), axis=-1, dtype=paddle.float32 if attn_output_weights.dtype == paddle.float16 else attn_output_weights.dtype) attn_output_weights = F.dropout(attn_output_weights, p=self.dropout, training=self.training) attn_output = paddle.bmm(attn_output_weights, v) assert list(attn_output.shape) == [bsz * self.num_heads, tgt_len, self.head_dim] attn_output = attn_output.transpose([1, 0,2]).reshape([tgt_len, bsz, embed_dim]) attn_output = self.out_proj(attn_output) if need_weights: # average attention weights over heads attn_output_weights = attn_output_weights.reshape([bsz, self.num_heads, tgt_len, src_len]) attn_output_weights = attn_output_weights.sum(axis=1) / self.num_heads else: attn_output_weights = None return attn_output, attn_output_weights def _in_proj_q(self, query): query = query.transpose([1, 2, 0]) query = paddle.unsqueeze(query, axis=2) res = self.conv1(query) res = paddle.squeeze(res, axis=2) res = res.transpose([2, 0, 1]) return res def _in_proj_k(self, key): key = key.transpose([1, 2, 0]) key = paddle.unsqueeze(key, axis=2) res = self.conv2(key) res = paddle.squeeze(res, axis=2) res = res.transpose([2, 0, 1]) return res def _in_proj_v(self, value): value = value.transpose([1,2,0])#(1, 2, 0) value = paddle.unsqueeze(value, axis=2) res = self.conv3(value) res = paddle.squeeze(res, axis=2) res = res.transpose([2, 0, 1]) return res