diff --git a/README.md b/README.md index 15d9a52..2610aba 100644 --- a/README.md +++ b/README.md @@ -2213,4 +2213,16 @@ Coming from computer vision and new to transformers? Here are some resources tha } ``` +```bibtex +@misc{gopalakrishnan2025decouplingwhatwherepolar, + title = {Decoupling the "What" and "Where" With Polar Coordinate Positional Embeddings}, + author = {Anand Gopalakrishnan and Robert Csordás and Jürgen Schmidhuber and Michael C. Mozer}, + year = {2025}, + eprint = {2509.10534}, + archivePrefix = {arXiv}, + primaryClass = {cs.LG}, + url = {https://arxiv.org/abs/2509.10534}, +} +``` + *I visualise a time when we will be to robots what dogs are to humans, and I’m rooting for the machines.* — Claude Shannon diff --git a/pyproject.toml b/pyproject.toml index b0959d0..e85b61c 100644 --- a/pyproject.toml +++ b/pyproject.toml @@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta" [project] name = "vit-pytorch" -version = "1.16.5" +version = "1.17.0" description = "Vision Transformer (ViT) - Pytorch" readme = { file = "README.md", content-type = "text/markdown" } license = { file = "LICENSE" } diff --git a/vit_pytorch/vit_nd_pope.py b/vit_pytorch/vit_nd_pope.py new file mode 100644 index 0000000..fd19a97 --- /dev/null +++ b/vit_pytorch/vit_nd_pope.py @@ -0,0 +1,353 @@ +from __future__ import annotations + +import torch +import torch.nn.functional as F +from torch import pi, nn, arange, cat, stack, Tensor +from torch.nn import Module, ModuleList +from torch.amp import autocast + +from einops import rearrange, repeat, reduce, pack, unpack +from einops.layers.torch import Rearrange + +# helpers + +def exists(val): + return val is not None + +def l2norm(t): + return F.normalize(t, dim = -1, p = 2) + +def join(arr, delimiter = ' '): + return delimiter.join(arr) + +def ensure_tuple(t, length): + if isinstance(t, (tuple, list)): + assert len(t) == length, f'Expected tuple of length {length}, got {len(t)}' + return tuple(t) + + return (t,) * length + +# golden gate rotary - Jerry Xiong, PhD student at UIUC +# https://jerryxio.ng/posts/nd-rope/ + +# but using polar version instead +# Gopalakrishnan et al. https://arxiv.org/abs/2509.10534 + +def _phi(m: int) -> float: + x = 2.0 + for _ in range(10): + x = (1 + x) ** (1.0 / (m + 1.0)) + return x + +def make_directions(n: int, d: int) -> Tensor: + g = _phi(d) + alpha = (1.0 / g) ** arange(1, d + 1, dtype = torch.float64) + i = arange(1, n + 1, dtype = torch.float64).unsqueeze(1) + z = torch.fmod(i * alpha, 1.0) + directions = torch.erfinv(2.0 * z - 1.0) + directions = l2norm(directions) + return directions.float() + +class GoldenGatePoPENd(Module): + def __init__( + self, + dim_pos: int, + heads: int, + dim_head: int, + min_freq: float = 1.0, + max_freq: float = 10000.0, + p_zero_freqs: float = 0.0, # proportion of frequencies set to 0 + init_learned_bias_uniform = False + ): + super().__init__() + n_freqs = dim_head + n_zero_freqs = round(p_zero_freqs * n_freqs) + + omega = cat(( + torch.zeros(n_zero_freqs), + min_freq * (max_freq / min_freq) ** torch.linspace(0, 1, n_freqs - n_zero_freqs), + )) + + directions = rearrange( + make_directions(heads * n_freqs, dim_pos), + '(h f) p -> h f p', + h = heads + ) + + omega_expanded = rearrange(omega, 'f -> f 1') + self.register_buffer('freqs', directions * omega_expanded) # shape: (h, f, p) + + self.learned_bias = nn.Parameter(torch.zeros(heads, dim_head)) + + if init_learned_bias_uniform: + self.learned_bias.uniform_(-2. * pi, 0.) + + @autocast('cuda', enabled = False) + def forward(self, pos): + + freqs = rearrange(self.freqs, 'h f p -> 1 h 1 f p') + positions = rearrange(pos.float(), 'b n p -> b 1 n 1 p') + + # compute theta for each (batch, head, seq, freq) + + theta = reduce(freqs * positions, 'b h n f p -> b h n f', 'sum') + + bias = self.learned_bias.clamp(-2. * pi, 0.) + bias = rearrange(bias, 'h d -> h 1 d') + + return theta, bias + +@autocast('cuda', enabled = False) +def apply_polar_pos_emb(t, freqs): + rot_dim, seq_len, orig_dtype = freqs.shape[-1], t.shape[-2], t.dtype + freqs = freqs[:, -seq_len:] + + t = t.float() + + t = F.softplus(t) + out = cat((t * freqs.cos(), t * freqs.sin()), dim = -1) + + return out.type(orig_dtype) + +# classes + +class FeedForward(Module): + def __init__(self, dim, hidden_dim, dropout = 0.): + super().__init__() + self.net = nn.Sequential( + nn.LayerNorm(dim), + nn.Linear(dim, hidden_dim), + nn.GELU(), + nn.Dropout(dropout), + nn.Linear(hidden_dim, dim), + nn.Dropout(dropout) + ) + + def forward(self, x): + return self.net(x) + +class Attention(Module): + def __init__(self, dim, heads = 8, dim_head = 64, dropout = 0.): + super().__init__() + inner_dim = dim_head * heads + project_out = not (heads == 1 and dim_head == dim) + + self.heads = heads + self.scale = dim_head ** -0.5 + + self.norm = nn.LayerNorm(dim) + self.attend = nn.Softmax(dim = -1) + self.dropout = nn.Dropout(dropout) + + self.to_qk = nn.Linear(dim, inner_dim * 2, bias = False) + self.to_v = nn.Linear(dim, inner_dim, bias = False) + + self.to_out = nn.Sequential( + nn.Linear(inner_dim, dim), + nn.Dropout(dropout) + ) if project_out else nn.Identity() + + def forward(self, x, polar_pos_emb = None): + x = self.norm(x) + qkv = (*self.to_qk(x).chunk(2, dim = -1), self.to_v(x)) + + q, k, v = map(lambda t: rearrange(t, 'b n (h d) -> b h n d', h = self.heads), qkv) + + if exists(polar_pos_emb): + freqs, bias = polar_pos_emb + q = apply_polar_pos_emb(q, freqs) + k = apply_polar_pos_emb(k, freqs + bias) + + dots = torch.matmul(q, k.transpose(-1, -2)) * self.scale + + attn = self.attend(dots) + attn = self.dropout(attn) + + out = torch.matmul(attn, v) + out = rearrange(out, 'b h n d -> b n (h d)') + return self.to_out(out) + +class Transformer(Module): + def __init__(self, dim, depth, heads, dim_head, mlp_dim, dropout = 0., polar_emb = None): + super().__init__() + self.norm = nn.LayerNorm(dim) + + self.polar_emb = polar_emb + + self.layers = ModuleList([]) + + for _ in range(depth): + self.layers.append(ModuleList([ + Attention(dim, heads = heads, dim_head = dim_head, dropout = dropout), + FeedForward(dim, mlp_dim, dropout = dropout) + ])) + + def forward(self, x, pos = None): + + # pope embedding + + polar_pos_emb = None + if exists(pos) and exists(self.polar_emb): + polar_pos_emb = self.polar_emb(pos) + + # transformer layers + + for attn, ff in self.layers: + x = attn(x, polar_pos_emb) + x + x = ff(x) + x + + return self.norm(x) + +class ViTND(Module): + def __init__( + self, + *, + ndim: int, + input_shape: int | tuple[int, ...], + patch_size: int | tuple[int, ...], + num_classes: int, + dim: int, + depth: int, + heads: int, + mlp_dim: int, + channels: int = 3, + dim_head: int = 64, + dropout: float = 0., + emb_dropout: float = 0., + pope_min_freq: float = 1.0, + pope_max_freq: float = 10000.0, + pope_p_zero_freqs: float = 0.0, + pope_init_learned_bias_uniform = False + ): + super().__init__() + + assert 1 <= ndim <= 7, 'ndim must be between 1 and 7' + + self.ndim = ndim + + input_shape = ensure_tuple(input_shape, ndim) + patch_size = ensure_tuple(patch_size, ndim) + + for i, (inp_dim, patch_dim) in enumerate(zip(input_shape, patch_size)): + assert inp_dim % patch_dim == 0, f'Input dimension {i} ({inp_dim}) must be divisible by patch size ({patch_dim})' + + num_patches_per_dim = [inp_dim // patch_dim for inp_dim, patch_dim in zip(input_shape, patch_size)] + num_patches = 1 + for n in num_patches_per_dim: + num_patches *= n + + patch_dim = channels + for p in patch_size: + patch_dim *= p + + dim_names = 'fghijkl'[:ndim] + + input_dims = [f'({d} p{i})' for i, d in enumerate(dim_names)] + patch_dims = [f'p{i}' for i in range(ndim)] + + input_pattern = f'b c {join(input_dims)}' + output_pattern = f'b {join(dim_names)} ({join(patch_dims)} c)' + rearrange_str = f'{input_pattern} -> {output_pattern}' + + rearrange_kwargs = {f'p{i}': p for i, p in enumerate(patch_size)} + + self.to_patch_embedding = nn.Sequential( + Rearrange(rearrange_str, **rearrange_kwargs), + nn.Linear(patch_dim, dim), + nn.LayerNorm(dim), + ) + + self.dropout = nn.Dropout(emb_dropout) + + # golden gate pope + + self.polar_emb = GoldenGatePoPENd( + dim_pos = ndim, + heads = heads, + dim_head = dim_head, + min_freq = pope_min_freq, + max_freq = pope_max_freq, + p_zero_freqs = pope_p_zero_freqs, + init_learned_bias_uniform = pope_init_learned_bias_uniform + ) + + self.transformer = Transformer(dim, depth, heads, dim_head, mlp_dim, dropout, polar_emb = self.polar_emb) + + self.to_latent = nn.Identity() + self.mlp_head = nn.Linear(dim, num_classes) + + def muon_parameters(self): + params = [] + + for m in self.modules(): + if isinstance(m, Attention): + params.extend([ + m.to_v.weight, + m.to_out[0].weight + ]) + elif isinstance(m, FeedForward): + params.extend([ + m.net[1].weight, + m.net[-2].weight + ]) + + return params + + def forward( + self, + x, + return_embed = False + ): + x = self.to_patch_embedding(x) # (b, *spatial_dims, patch_dim) + + batch, *spatial_dims, _, device = *x.shape, x.device + + # Generate position coordinates + + grids = [arange(d, device = device, dtype = torch.float32) for d in spatial_dims] + grid = torch.meshgrid(*grids, indexing = 'ij') + pos = stack(grid, dim = -1) # (*spatial_dims, ndim) + + # flatten spatial dimensions for attention with nd rotary + + pos = repeat(pos, '... p -> b (...) p', b = batch) + x, packed_shape = pack([x], 'b * d') + + x = self.dropout(x) + + embed = self.transformer(x, pos) + + # return the embed with reconstituted patch shape + + if return_embed: + embed, = unpack(embed, packed_shape, 'b * d') + return embed + + # pooling to logits + + pooled = reduce(embed, 'b n d -> b d', 'mean') + + pooled = self.to_latent(pooled) + return self.mlp_head(pooled) + +if __name__ == '__main__': + + model = ViTND( + ndim = 5, + input_shape = (4, 8, 16, 32, 64), + patch_size = (2, 2, 4, 4, 8), + num_classes = 1000, + dim = 512, + depth = 6, + heads = 8, + mlp_dim = 2048, + channels = 3, + dropout = 0.1, + emb_dropout = 0.1 + ) + + data = torch.randn(3, 3, 4, 8, 16, 32, 64) + + logits = model(data) + + embed = model(data, return_embed = True) # (2, 2, 4, 4, 8, 8, 512)