48 lines
1.9 KiB
Python
48 lines
1.9 KiB
Python
from typing import *
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import torch
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import torch.nn as nn
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class RotaryPositionEmbedder(nn.Module):
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def __init__(
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self,
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head_dim: int,
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dim: int = 3,
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rope_freq: Tuple[float, float] = (1.0, 10000.0)
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):
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super().__init__()
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assert head_dim % 2 == 0, "Head dim must be divisible by 2"
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self.head_dim = head_dim
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self.dim = dim
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self.rope_freq = rope_freq
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self.freq_dim = head_dim // 2 // dim
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self.freqs = torch.arange(self.freq_dim, dtype=torch.float32) / self.freq_dim
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self.freqs = rope_freq[0] / (rope_freq[1] ** (self.freqs))
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def _get_phases(self, indices: torch.Tensor) -> torch.Tensor:
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self.freqs = self.freqs.to(indices.device)
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phases = torch.outer(indices, self.freqs)
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phases = torch.polar(torch.ones_like(phases), phases)
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return phases
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@staticmethod
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def apply_rotary_embedding(x: torch.Tensor, phases: torch.Tensor) -> torch.Tensor:
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x_complex = torch.view_as_complex(x.float().reshape(*x.shape[:-1], -1, 2))
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x_rotated = x_complex * phases.unsqueeze(-2)
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x_embed = torch.view_as_real(x_rotated).reshape(*x_rotated.shape[:-1], -1).to(x.dtype)
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return x_embed
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def forward(self, indices: torch.Tensor) -> torch.Tensor:
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"""
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Args:
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indices (torch.Tensor): [..., N, C] tensor of spatial positions
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"""
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assert indices.shape[-1] == self.dim, f"Last dim of indices must be {self.dim}"
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phases = self._get_phases(indices.reshape(-1)).reshape(*indices.shape[:-1], -1)
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if phases.shape[-1] < self.head_dim // 2:
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padn = self.head_dim // 2 - phases.shape[-1]
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phases = torch.cat([phases, torch.polar(
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torch.ones(*phases.shape[:-1], padn, device=phases.device),
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torch.zeros(*phases.shape[:-1], padn, device=phases.device)
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)], dim=-1)
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return phases |