Added multi-vector embeddings

8 files changed, 299 insertions, 81 deletions

diff --git a/common.py b/common.py
index f369475..e8d3ac1 100644
--- a/common.py
+++ b/common.py
@@ -1,9 +1,10 @@
 from pathlib import Path
 import json
 
-import torch
+from models.clip.embeddings import ManagedCLIPTextEmbeddings
+from models.clip.tokenizer import MultiCLIPTokenizer
 
-from transformers import CLIPTextModel, CLIPTokenizer
+from safetensors import safe_open
 
 
 def load_config(filename):
@@ -18,33 +19,20 @@ def load_config(filename):
     return args
 
 
-def load_text_embedding(embeddings, token_id, file):
-    data = torch.load(file, map_location="cpu")
-
-    assert len(data.keys()) == 1, 'embedding data has multiple terms in it'
-
-    emb = next(iter(data.values()))
-    if len(emb.shape) == 1:
-        emb = emb.unsqueeze(0)
-
-    embeddings[token_id] = emb
-
-
-def load_text_embeddings(tokenizer: CLIPTokenizer, text_encoder: CLIPTextModel, embeddings_dir: Path):
+def load_embeddings_from_dir(tokenizer: MultiCLIPTokenizer, embeddings: ManagedCLIPTextEmbeddings, embeddings_dir: Path):
     if not embeddings_dir.exists() or not embeddings_dir.is_dir():
         return []
 
-    files = [file for file in embeddings_dir.iterdir() if file.is_file()]
-
-    tokens = [file.stem for file in files]
-    added = tokenizer.add_tokens(tokens)
-    token_ids = tokenizer.convert_tokens_to_ids(tokens)
-
-    text_encoder.resize_token_embeddings(len(tokenizer))
+    filenames = [filename for filename in embeddings_dir.iterdir() if filename.is_file()]
+    tokens = [filename.stem for filename in filenames]
 
-    token_embeds = text_encoder.get_input_embeddings().weight.data
+    for filename in embeddings_dir.iterdir():
+        if filename.is_file():
+            with safe_open(filename, framework="pt", device="cpu") as file:
+                embed = file.get_tensor("embed")
 
-    for (token_id, file) in zip(token_ids, files):
-        load_text_embedding(token_embeds, token_id, file)
+                added = tokenizer.add_multi_tokens(filename.stem, embed.shape[0])
+                embeddings.add_embed(added.placeholder_id)
+                embeddings.add_embed(added.multi_ids, embed)
 
     return tokens
diff --git a/environment.yaml b/environment.yaml
index c006379..7f0e903 100644
--- a/environment.yaml
+++ b/environment.yaml
@@ -18,6 +18,7 @@ dependencies:
       - accelerate==0.15.0
       - bitsandbytes==0.35.4
       - python-slugify>=6.1.2
+      - safetensors==0.2.7
       - setuptools==65.6.3
       - test-tube>=0.7.5
       - transformers==4.25.1
diff --git a/infer.py b/infer.py
index ae0b4da..4bcaff5 100644
--- a/infer.py
+++ b/infer.py
@@ -8,6 +8,7 @@ from pathlib import Path
 import torch
 import json
 from PIL import Image
+from slugify import slugify
 from diffusers import (
     AutoencoderKL,
     UNet2DConditionModel,
@@ -20,11 +21,12 @@ from diffusers import (
     KDPM2DiscreteScheduler,
     KDPM2AncestralDiscreteScheduler
 )
-from transformers import CLIPTextModel, CLIPTokenizer
-from slugify import slugify
+from transformers import CLIPTextModel
 
+from models.clip.embeddings import patch_managed_embeddings
+from models.clip.tokenizer import MultiCLIPTokenizer
 from pipelines.stable_diffusion.vlpn_stable_diffusion import VlpnStableDiffusion
-from common import load_text_embeddings, load_config
+from common import load_config, load_embeddings_from_dir
 
 
 torch.backends.cuda.matmul.allow_tf32 = True
@@ -183,13 +185,15 @@ def save_args(basepath, args, extra={}):
 def create_pipeline(model, embeddings_dir, dtype):
     print("Loading Stable Diffusion pipeline...")
 
-    tokenizer = CLIPTokenizer.from_pretrained(model, subfolder='tokenizer', torch_dtype=dtype)
+    tokenizer = MultiCLIPTokenizer.from_pretrained(model, subfolder='tokenizer', torch_dtype=dtype)
     text_encoder = CLIPTextModel.from_pretrained(model, subfolder='text_encoder', torch_dtype=dtype)
     vae = AutoencoderKL.from_pretrained(model, subfolder='vae', torch_dtype=dtype)
     unet = UNet2DConditionModel.from_pretrained(model, subfolder='unet', torch_dtype=dtype)
     scheduler = DDIMScheduler.from_pretrained(model, subfolder='scheduler', torch_dtype=dtype)
 
-    added_tokens = load_text_embeddings(tokenizer, text_encoder, Path(embeddings_dir))
+    embeddings = patch_managed_embeddings(text_encoder)
+    added_tokens = load_embeddings_from_dir(tokenizer, embeddings, Path(embeddings_dir))
+
     print(f"Added {len(added_tokens)} tokens from embeddings dir: {added_tokens}")
 
     pipeline = VlpnStableDiffusion(
diff --git a/models/clip/embeddings.py b/models/clip/embeddings.py
new file mode 100644
index 0000000..7d63ffb
--- /dev/null
+++ b/models/clip/embeddings.py
@@ -0,0 +1,109 @@
+from typing import Union, Optional
+from pathlib import Path
+
+import torch
+import torch.nn as nn
+
+from safetensors import safe_open
+from safetensors.torch import save_file
+
+from transformers import CLIPTextModel
+from transformers.models.clip import CLIPTextConfig
+from transformers.models.clip.modeling_clip import CLIPTextEmbeddings
+
+
+def expand_embedding(old_embedding: nn.Embedding, n: int) -> nn.Embedding:
+    old_num_embeddings, old_embedding_dim = old_embedding.weight.size()
+
+    new_embedding = nn.Embedding(old_num_embeddings + n, old_embedding_dim)
+    new_embedding.to(old_embedding.weight.device, dtype=old_embedding.weight.dtype)
+    new_embedding.weight.data.zero_()
+    new_embedding.weight.data[:old_num_embeddings] = old_embedding.weight.data
+
+    return new_embedding
+
+
+class ManagedCLIPTextEmbeddings(CLIPTextEmbeddings):
+    def __init__(self, config: CLIPTextConfig, embeddings: CLIPTextEmbeddings):
+        super().__init__(config)
+
+        self.token_embedding = embeddings.token_embedding
+        self.position_embedding = embeddings.position_embedding
+
+        self.temp_token_embedding = nn.Embedding(
+            self.token_embedding.num_embeddings, self.token_embedding.embedding_dim)
+        self.temp_token_embedding.weight.data.zero_()
+        self.temp_token_ids = torch.tensor([])
+
+    def add_embed(self, token_ids: Union[int, list[int]], initializer: Optional[Union[int, list[int], torch.FloatTensor]] = None):
+        if isinstance(token_ids, int):
+            token_ids = [token_ids]
+
+        if initializer is not None:
+            if isinstance(initializer, int):
+                initializer = [initializer]
+
+            if isinstance(initializer, list):
+                initializer = (initializer * len(token_ids))[:len(token_ids)]
+
+                with torch.no_grad():
+                    initializer = self.get_embed(initializer)
+
+        self.temp_token_embedding = expand_embedding(self.temp_token_embedding, len(token_ids))
+        self.token_embedding = expand_embedding(self.token_embedding, len(token_ids))
+
+        token_ids = torch.tensor(token_ids)
+
+        self.temp_token_ids = torch.cat([self.temp_token_ids, token_ids])
+
+        if initializer is not None:
+            self.temp_token_embedding.weight.data[token_ids] = initializer
+        else:
+            self.temp_token_embedding.weight.data[token_ids].zero_()
+
+    def load_embed(self, input_ids: list[int], filename: Path):
+        with safe_open(filename, framework="pt", device="cpu") as file:
+            self.add_embed(input_ids, file.get_tensor("embed"))
+
+    def save_embed(self, input_ids: list[int], filename: Path):
+        save_file({"embed": self.get_embed(input_ids)}, filename)
+
+    def make_permanent(self):
+        self.token_embedding.weight.data[self.temp_token_ids] = self.temp_token_embedding.weight.data[self.temp_token_ids]
+        self.temp_token_ids = torch.tensor([])
+
+    def get_embed(self, input_ids: Union[list[int], torch.LongTensor]):
+        if isinstance(input_ids, list):
+            input_ids = torch.tensor(input_ids)
+
+        mask = torch.isin(input_ids, torch.tensor(self.temp_token_ids, device=input_ids.device))
+
+        embeds = self.token_embedding(input_ids)
+        embeds[mask] = self.temp_token_embedding(input_ids)[mask]
+
+        return embeds
+
+    def forward(
+        self,
+        input_ids: Optional[torch.LongTensor] = None,
+        position_ids: Optional[torch.LongTensor] = None,
+        inputs_embeds: Optional[torch.FloatTensor] = None,
+    ) -> torch.Tensor:
+        seq_length = input_ids.shape[-1] if input_ids is not None else inputs_embeds.shape[-2]
+
+        if position_ids is None:
+            position_ids = self.position_ids[:, :seq_length]
+
+        if inputs_embeds is None:
+            inputs_embeds = self.get_embed(input_ids)
+
+        position_embeddings = self.position_embedding(position_ids)
+        embeddings = inputs_embeds + position_embeddings
+
+        return embeddings
+
+
+def patch_managed_embeddings(text_encoder: CLIPTextModel) -> ManagedCLIPTextEmbeddings:
+    text_embeddings = ManagedCLIPTextEmbeddings(text_encoder.config, text_encoder.text_model.embeddings)
+    text_encoder.text_model.embeddings = text_embeddings
+    return text_embeddings
diff --git a/models/clip/prompt.py b/models/clip/prompt.py
index da33ecf..9da3955 100644
--- a/models/clip/prompt.py
+++ b/models/clip/prompt.py
@@ -1,4 +1,4 @@
-from typing import List, Union
+from typing import Union
 
 import torch
 
@@ -10,13 +10,13 @@ class PromptProcessor():
         self.tokenizer = tokenizer
         self.text_encoder = text_encoder
 
-    def get_input_ids(self, prompt: Union[str, List[str]]):
+    def get_input_ids(self, prompt: Union[str, list[str]]):
         return self.tokenizer(
             prompt,
             padding="do_not_pad",
         ).input_ids
 
-    def unify_input_ids(self, input_ids: List[int]):
+    def unify_input_ids(self, input_ids: list[int]):
         return self.tokenizer.pad(
             {"input_ids": input_ids},
             padding=True,
diff --git a/models/clip/tokenizer.py b/models/clip/tokenizer.py
new file mode 100644
index 0000000..78871db
--- /dev/null
+++ b/models/clip/tokenizer.py
@@ -0,0 +1,64 @@
+import copy
+from typing import NamedTuple, Union
+
+import numpy as np
+
+from transformers import CLIPTokenizer
+
+
+class MultiCLIPTokenizerItem(NamedTuple):
+    token: str
+    placeholder_id: int
+    multi_ids: list[int]
+
+
+class MultiCLIPTokenizer(CLIPTokenizer):
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.token_map: dict[int, list[int]] = {}
+
+    def add_multi_tokens(self, new_tokens: Union[str, list[str]], num_vectors: Union[int, list[int]] = 1) -> MultiCLIPTokenizerItem:
+        if isinstance(new_tokens, list):
+            if isinstance(num_vectors, int):
+                num_vectors = [num_vectors] * len(new_tokens)
+
+            if len(num_vectors) != len(new_tokens):
+                raise ValueError("Expected new_tokens and num_vectors to have the same len")
+
+            return [self.add_multi_tokens(new_token, vecs) for new_token, vecs in zip(new_tokens, num_vectors)]
+
+        if isinstance(num_vectors, list):
+            raise ValueError("Expected num_vectors to be int for single token")
+
+        super().add_tokens(new_tokens)
+
+        if num_vectors == 1:
+            multi_token = [new_tokens]
+        else:
+            multi_token = [f"{new_tokens}_{i}" for i in range(num_vectors)]
+            super().add_tokens(multi_token)
+
+        meta_id = super().convert_tokens_to_ids(new_tokens)
+        multi_ids = super().convert_tokens_to_ids(multi_token)
+
+        self.token_map[meta_id] = multi_ids
+
+        return MultiCLIPTokenizerItem(new_tokens, meta_id, multi_ids)
+
+    def encode(self, *args, vector_shuffle=True, **kwargs):
+        ids = super().encode(*args, **kwargs)
+        new_ids = []
+
+        for id in ids:
+            if id in self.token_map:
+                tokens = self.token_map[id]
+
+                if vector_shuffle:
+                    tokens = copy.copy(tokens)
+                    np.random.shuffle(tokens)
+
+                new_ids = new_ids + self.token_map[id]
+            else:
+                new_ids.append(id)
+
+        return new_ids
diff --git a/train_ti.py b/train_ti.py
index 088c1a6..69d15ea 100644
--- a/train_ti.py
+++ b/train_ti.py
@@ -16,17 +16,18 @@ from diffusers import AutoencoderKL, DDPMScheduler, DPMSolverMultistepScheduler,
 from diffusers.optimization import get_scheduler, get_cosine_with_hard_restarts_schedule_with_warmup
 import matplotlib.pyplot as plt
 from tqdm.auto import tqdm
-from transformers import CLIPTextModel, CLIPTokenizer
+from transformers import CLIPTextModel
 from slugify import slugify
 
-from common import load_text_embeddings, load_text_embedding, load_config
+from common import load_config, load_embeddings_from_dir
 from pipelines.stable_diffusion.vlpn_stable_diffusion import VlpnStableDiffusion
 from data.csv import CSVDataModule, CSVDataItem
 from training.optimization import get_one_cycle_schedule
 from training.lr import LRFinder
-from training.ti import patch_trainable_embeddings
 from training.util import AverageMeter, CheckpointerBase, save_args
+from models.clip.embeddings import patch_managed_embeddings
 from models.clip.prompt import PromptProcessor
+from models.clip.tokenizer import MultiCLIPTokenizer
 
 logger = get_logger(__name__)
 
@@ -81,6 +82,12 @@ def parse_args():
         help="A token to use as initializer word."
     )
     parser.add_argument(
+        "--num_vectors",
+        type=int,
+        nargs='*',
+        help="Number of vectors per embedding."
+    )
+    parser.add_argument(
         "--num_class_images",
         type=int,
         default=1,
@@ -360,8 +367,17 @@ def parse_args():
     if len(args.placeholder_token) == 0:
         args.placeholder_token = [f"<*{i}>" for i in range(args.initializer_token)]
 
+    if args.num_vectors is None:
+        args.num_vectors = 1
+
+    if isinstance(args.num_vectors, int):
+        args.num_vectors = [args.num_vectors] * len(args.initializer_token)
+
     if len(args.placeholder_token) != len(args.initializer_token):
-        raise ValueError("You must specify --placeholder_token")
+        raise ValueError("--placeholder_token and --initializer_token must have the same number of items")
+
+    if len(args.placeholder_token) != len(args.num_vectors):
+        raise ValueError("--placeholder_token and --num_vectors must have the same number of items")
 
     if isinstance(args.collection, str):
         args.collection = [args.collection]
@@ -386,8 +402,7 @@ class Checkpointer(CheckpointerBase):
         tokenizer,
         text_encoder,
         scheduler,
-        placeholder_token,
-        placeholder_token_id,
+        new_tokens,
         output_dir: Path,
         sample_image_size,
         sample_batches,
@@ -397,8 +412,6 @@ class Checkpointer(CheckpointerBase):
         super().__init__(
             datamodule=datamodule,
             output_dir=output_dir,
-            placeholder_token=placeholder_token,
-            placeholder_token_id=placeholder_token_id,
             sample_image_size=sample_image_size,
             seed=seed or torch.random.seed(),
             sample_batches=sample_batches,
@@ -412,6 +425,7 @@ class Checkpointer(CheckpointerBase):
         self.tokenizer = tokenizer
         self.text_encoder = text_encoder
         self.scheduler = scheduler
+        self.new_tokens = new_tokens
 
     @torch.no_grad()
     def checkpoint(self, step, postfix):
@@ -422,13 +436,11 @@ class Checkpointer(CheckpointerBase):
 
         text_encoder = self.accelerator.unwrap_model(self.text_encoder)
 
-        for (placeholder_token, placeholder_token_id) in zip(self.placeholder_token, self.placeholder_token_id):
-            # Save a checkpoint
-            learned_embeds = text_encoder.text_model.embeddings.trainable_embedding.weight.data[placeholder_token_id]
-            learned_embeds_dict = {placeholder_token: learned_embeds.detach().cpu()}
-
-            filename = f"%s_%d_%s.bin" % (slugify(placeholder_token), step, postfix)
-            torch.save(learned_embeds_dict, checkpoints_path.joinpath(filename))
+        for new_token in self.new_tokens:
+            text_encoder.text_model.embeddings.save_embed(
+                new_token.multi_ids,
+                f"{slugify(new_token.token)}_{step}_{postfix}.bin"
+            )
 
         del text_encoder
         del learned_embeds
@@ -487,9 +499,9 @@ def main():
 
     # Load the tokenizer and add the placeholder token as a additional special token
     if args.tokenizer_name:
-        tokenizer = CLIPTokenizer.from_pretrained(args.tokenizer_name)
+        tokenizer = MultiCLIPTokenizer.from_pretrained(args.tokenizer_name)
     elif args.pretrained_model_name_or_path:
-        tokenizer = CLIPTokenizer.from_pretrained(args.pretrained_model_name_or_path, subfolder='tokenizer')
+        tokenizer = MultiCLIPTokenizer.from_pretrained(args.pretrained_model_name_or_path, subfolder='tokenizer')
 
     # Load models and create wrapper for stable diffusion
     text_encoder = CLIPTextModel.from_pretrained(args.pretrained_model_name_or_path, subfolder='text_encoder')
@@ -507,45 +519,33 @@ def main():
         unet.enable_gradient_checkpointing()
         text_encoder.gradient_checkpointing_enable()
 
+    embeddings = patch_managed_embeddings(text_encoder)
+
     if args.embeddings_dir is not None:
         embeddings_dir = Path(args.embeddings_dir)
         if not embeddings_dir.exists() or not embeddings_dir.is_dir():
             raise ValueError("--embeddings_dir must point to an existing directory")
-        added_tokens_from_dir = load_text_embeddings(tokenizer, text_encoder, embeddings_dir)
+
+        added_tokens_from_dir = load_embeddings_from_dir(tokenizer, embeddings, embeddings_dir)
         print(f"Added {len(added_tokens_from_dir)} tokens from embeddings dir: {added_tokens_from_dir}")
 
     # Convert the initializer_token, placeholder_token to ids
-    initializer_token_ids = torch.stack([
-        torch.tensor(tokenizer.encode(token, add_special_tokens=False)[:1])
+    initializer_token_ids = [
+        tokenizer.encode(token, add_special_tokens=False)
         for token in args.initializer_token
-    ])
-
-    num_added_tokens = tokenizer.add_tokens(args.placeholder_token)
-    print(f"Added {num_added_tokens} new tokens.")
-
-    placeholder_token_id = tokenizer.convert_tokens_to_ids(args.placeholder_token)
+    ]
 
-    # Resize the token embeddings as we are adding new special tokens to the tokenizer
-    text_encoder.resize_token_embeddings(len(tokenizer))
+    new_tokens = tokenizer.add_multi_tokens(args.placeholder_token, args.num_vectors)
 
-    # Initialise the newly added placeholder token with the embeddings of the initializer token
-    token_embeds = text_encoder.get_input_embeddings().weight.data
+    for (new_token, init_ids) in zip(new_tokens, initializer_token_ids):
+        embeddings.add_embed(new_token.placeholder_id)
+        embeddings.add_embed(new_token.multi_ids, init_ids)
 
-    if args.resume_from is not None:
-        resumepath = Path(args.resume_from).joinpath("checkpoints")
-
-        for (token_id, token) in zip(placeholder_token_id, args.placeholder_token):
-            load_text_embedding(token_embeds, token_id, resumepath.joinpath(f"{token}_{args.global_step}_end.bin"))
-
-    initializer_token_embeddings = text_encoder.get_input_embeddings()(initializer_token_ids)
-    for (token_id, embeddings) in zip(placeholder_token_id, initializer_token_embeddings):
-        token_embeds[token_id] = embeddings
+    print(f"Added {len(new_tokens)} new tokens.")
 
     vae.requires_grad_(False)
     unet.requires_grad_(False)
 
-    patch_trainable_embeddings(text_encoder, placeholder_token_id)
-
     text_encoder.text_model.encoder.requires_grad_(False)
     text_encoder.text_model.final_layer_norm.requires_grad_(False)
     text_encoder.text_model.embeddings.position_embedding.requires_grad_(False)
@@ -575,7 +575,7 @@ def main():
 
     # Initialize the optimizer
     optimizer = optimizer_class(
-        text_encoder.text_model.embeddings.trainable_embedding.parameters(),  # only optimize the embeddings
+        text_encoder.text_model.embeddings.temp_token_embedding.parameters(),  # only optimize the embeddings
         lr=args.learning_rate,
         betas=(args.adam_beta1, args.adam_beta2),
         weight_decay=args.adam_weight_decay,
@@ -816,6 +816,7 @@ def main():
         config = vars(args).copy()
         config["initializer_token"] = " ".join(config["initializer_token"])
         config["placeholder_token"] = " ".join(config["placeholder_token"])
+        config["num_vectors"] = " ".join([str(n) for n in config["num_vectors"]])
         if config["collection"] is not None:
             config["collection"] = " ".join(config["collection"])
         if config["exclude_collections"] is not None:
@@ -852,8 +853,7 @@ def main():
         tokenizer=tokenizer,
         text_encoder=text_encoder,
         scheduler=checkpoint_scheduler,
-        placeholder_token=args.placeholder_token,
-        placeholder_token_id=placeholder_token_id,
+        new_tokens=new_tokens,
         output_dir=basepath,
         sample_image_size=args.sample_image_size,
         sample_batch_size=args.sample_batch_size,
diff --git a/training/util.py b/training/util.py
index d0f7fcd..43a55e1 100644
--- a/training/util.py
+++ b/training/util.py
@@ -1,5 +1,6 @@
 from pathlib import Path
 import json
+from typing import Iterable
 
 import torch
 from PIL import Image
@@ -39,8 +40,6 @@ class CheckpointerBase:
         self,
         datamodule,
         output_dir: Path,
-        placeholder_token,
-        placeholder_token_id,
         sample_image_size,
         sample_batches,
         sample_batch_size,
@@ -48,8 +47,6 @@ class CheckpointerBase:
     ):
         self.datamodule = datamodule
         self.output_dir = output_dir
-        self.placeholder_token = placeholder_token
-        self.placeholder_token_id = placeholder_token_id
         self.sample_image_size = sample_image_size
         self.seed = seed or torch.random.seed()
         self.sample_batches = sample_batches
@@ -117,3 +114,58 @@ class CheckpointerBase:
             del image_grid
 
         del generator
+
+
+class EMAModel:
+    """
+    Exponential Moving Average of models weights
+    """
+
+    def __init__(self, parameters: Iterable[torch.nn.Parameter], decay=0.9999):
+        parameters = list(parameters)
+        self.shadow_params = [p.clone().detach() for p in parameters]
+
+        self.decay = decay
+        self.optimization_step = 0
+
+    @torch.no_grad()
+    def step(self, parameters):
+        parameters = list(parameters)
+
+        self.optimization_step += 1
+
+        # Compute the decay factor for the exponential moving average.
+        value = (1 + self.optimization_step) / (10 + self.optimization_step)
+        one_minus_decay = 1 - min(self.decay, value)
+
+        for s_param, param in zip(self.shadow_params, parameters):
+            if param.requires_grad:
+                s_param.sub_(one_minus_decay * (s_param - param))
+            else:
+                s_param.copy_(param)
+
+        torch.cuda.empty_cache()
+
+    def copy_to(self, parameters: Iterable[torch.nn.Parameter]) -> None:
+        """
+        Copy current averaged parameters into given collection of parameters.
+        Args:
+            parameters: Iterable of `torch.nn.Parameter`; the parameters to be
+                updated with the stored moving averages. If `None`, the
+                parameters with which this `ExponentialMovingAverage` was
+                initialized will be used.
+        """
+        parameters = list(parameters)
+        for s_param, param in zip(self.shadow_params, parameters):
+            param.data.copy_(s_param.data)
+
+    def to(self, device=None, dtype=None) -> None:
+        r"""Move internal buffers of the ExponentialMovingAverage to `device`.
+        Args:
+            device: like `device` argument to `torch.Tensor.to`
+        """
+        # .to() on the tensors handles None correctly
+        self.shadow_params = [
+            p.to(device=device, dtype=dtype) if p.is_floating_point() else p.to(device=device)
+            for p in self.shadow_params
+        ]