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"""Absolute positional embedding."""
from einops import rearrange
import torch
from torch import nn
import torch.nn.functional as F
def l2norm(t, groups=1):
t = rearrange(t, "... (g d) -> ... g d", g=groups)
t = F.normalize(t, p=2, dim=-1)
return rearrange(t, "... g d -> ... (g d)")
class AbsolutePositionalEmbedding(nn.Module):
def __init__(self, dim, max_seq_len, l2norm_embed=False):
super().__init__()
self.scale = dim ** -0.5 if not l2norm_embed else 1.0
self.max_seq_len = max_seq_len
self.l2norm_embed = l2norm_embed
self.emb = nn.Embedding(max_seq_len, dim)
def forward(self, x, pos=None):
seq_len = x.shape[1]
assert (
seq_len <= self.max_seq_len
), f"you are passing in a sequence length of {seq_len} but your absolute positional embedding has a max sequence length of {self.max_seq_len}"
if pos is None:
pos = torch.arange(seq_len, device=x.device)
pos_emb = self.emb(pos)
pos_emb = pos_emb * self.scale
return l2norm(pos_emb) if self.l2norm_embed else pos_emb
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