Rework ID-based parametrisation

aurora/model/aurora.py

@@ -52,14 +52,11 @@ def __init__(
 
         Args:
             surf_vars (tuple[str, ...], optional): All surface-level variables supported by the
-                model. The model is sensitive to the order of `surf_vars`! Currently, adding
-                one more variable here causes the model to incorrectly load the static variables.
-                It is possible to hack around this. We are working on a more principled fix. Please
-                open an issue if this is a problem for you.
+                model.
             static_vars (tuple[str, ...], optional): All static variables supported by the
-                model. The model is sensitive to the order of `static_vars`!
+                model.
             atmos_vars (tuple[str, ...], optional): All atmospheric variables supported by the
-                model. The model is sensitive to the order of `atmos-vars`!
+                model.
             window_size (tuple[int, int, int], optional): Vertical height, height, and width of the
                 window of the underlying Swin transformer.
             encoder_depths (tuple[int, ...], optional): Number of blocks in each encoder layer.
@@ -231,12 +228,64 @@ def load_checkpoint(self, repo: str, name: str, strict: bool = True) -> None:
         path = hf_hub_download(repo_id=repo, filename=name)
         d = torch.load(path, map_location=device, weights_only=True)
 
-        # Rename keys to ensure compatibility.
+        # You can safely ignore all cumbersome processing below. We modified the model after we
+        # trained it. The code below manually adapts the checkpoints, so the checkpoints are
+        # compatible with the new model.
+
+        # Remove possibly prefix from the keys.
         for k, v in list(d.items()):
             if k.startswith("net."):
                 del d[k]
                 d[k[4:]] = v
 
+        # Convert the ID-based parametrisation to a name-based parametrisation.
+
+        if "encoder.surf_token_embeds.weight" in d:
+            weight = d["encoder.surf_token_embeds.weight"]
+            del d["encoder.surf_token_embeds.weight"]
+
+            assert weight.shape[1] == 4 + 3
+            for i, name in enumerate(("2t", "10u", "10v", "msl", "lsm", "z", "slt")):
+                d[f"encoder.surf_token_embeds.weights.{name}"] = weight[:, [i]]
+
+        if "encoder.atmos_token_embeds.weight" in d:
+            weight = d["encoder.atmos_token_embeds.weight"]
+            del d["encoder.atmos_token_embeds.weight"]
+
+            assert weight.shape[1] == 5
+            for i, name in enumerate(("z", "u", "v", "t", "q")):
+                d[f"encoder.atmos_token_embeds.weights.{name}"] = weight[:, [i]]
+
+        if "decoder.surf_head.weight" in d:
+            weight = d["decoder.surf_head.weight"]
+            bias = d["decoder.surf_head.bias"]
+            del d["decoder.surf_head.weight"]
+            del d["decoder.surf_head.bias"]
+
+            assert weight.shape[0] == 4 * self.patch_size**2
+            assert bias.shape[0] == 4 * self.patch_size**2
+            weight = weight.reshape(self.patch_size**2, 4, -1)
+            bias = bias.reshape(self.patch_size**2, 4)
+
+            for i, name in enumerate(("2t", "10u", "10v", "msl")):
+                d[f"decoder.surf_heads.{name}.weight"] = weight[:, i]
+                d[f"decoder.surf_heads.{name}.bias"] = bias[:, i]
+
+        if "decoder.atmos_head.weight" in d:
+            weight = d["decoder.atmos_head.weight"]
+            bias = d["decoder.atmos_head.bias"]
+            del d["decoder.atmos_head.weight"]
+            del d["decoder.atmos_head.bias"]
+
+            assert weight.shape[0] == 5 * self.patch_size**2
+            assert bias.shape[0] == 5 * self.patch_size**2
+            weight = weight.reshape(self.patch_size**2, 5, -1)
+            bias = bias.reshape(self.patch_size**2, 5)
+
+            for i, name in enumerate(("z", "u", "v", "t", "q")):
+                d[f"decoder.atmos_heads.{name}.weight"] = weight[:, i]
+                d[f"decoder.atmos_heads.{name}.bias"] = bias[:, i]
+
         self.load_state_dict(d, strict=strict)
 
 

aurora/model/decoder.py

@@ -11,8 +11,6 @@
 from aurora.model.perceiver import PerceiverResampler
 from aurora.model.util import (
     check_lat_lon_dtype,
-    create_var_map,
-    get_ids_for_var_map,
     init_weights,
     unpatchify,
 )
@@ -60,8 +58,6 @@ def __init__(
         self.patch_size = patch_size
         self.surf_vars = surf_vars
         self.atmos_vars = atmos_vars
-        self.surf_var_map = create_var_map(surf_vars)
-        self.atmos_var_map = create_var_map(atmos_vars)
         self.embed_dim = embed_dim
 
         self.level_decoder = PerceiverResampler(
@@ -76,8 +72,12 @@ def __init__(
             ln_eps=perceiver_ln_eps,
         )
 
-        self.surf_head = nn.Linear(embed_dim, len(surf_vars) * patch_size**2)
-        self.atmos_head = nn.Linear(embed_dim, len(atmos_vars) * patch_size**2)
+        self.surf_heads = nn.ParameterDict(
+            {name: nn.Linear(embed_dim, patch_size**2) for name in surf_vars}
+        )
+        self.atmos_heads = nn.ParameterDict(
+            {name: nn.Linear(embed_dim, patch_size**2) for name in atmos_vars}
+        )
 
         self.atmos_levels_embed = nn.Linear(embed_dim, embed_dim)
 
@@ -145,10 +145,10 @@ def forward(
             W=patch_res[2],
         )
 
-        # Decode surface vars.
-        x_surf = self.surf_head(x[..., :1, :])  # (B, L, 1, V_S*p*p)
-        surf_var_ids = get_ids_for_var_map(surf_vars, self.surf_var_map, x_surf.device)
-        surf_preds = unpatchify(x_surf, len(self.surf_vars), H, W, self.patch_size)[:, surf_var_ids]
+        # Decode surface vars. Run the head for every surface-level variable.
+        x_surf = torch.stack([self.surf_heads[name](x[..., :1, :]) for name in surf_vars], dim=-1)
+        x_surf = x_surf.reshape(*x_surf.shape[:3], -1)  # (B, L, 1, V_S*p*p)
+        surf_preds = unpatchify(x_surf, len(surf_vars), H, W, self.patch_size)
         surf_preds = surf_preds.squeeze(2)  # (B, V_S, H, W)
 
         # Embed the atmospheric levels.
@@ -162,10 +162,9 @@ def forward(
         x_atmos = self.deaggregate_levels(levels_embed, x[..., 1:, :])  # (B, L, C_A, D)
 
         # Decode the atmospheric vars.
-        x_atmos = self.atmos_head(x_atmos)  # (B, L, C_A, V_A*p*p)
-        atmos_var_ids = get_ids_for_var_map(atmos_vars, self.atmos_var_map, x.device)
-        atmos_preds = unpatchify(x_atmos, len(self.atmos_vars), H, W, self.patch_size)
-        atmos_preds = atmos_preds[:, atmos_var_ids]
+        x_atmos = torch.stack([self.atmos_heads[name](x_atmos) for name in atmos_vars], dim=-1)
+        x_atmos = x_atmos.reshape(*x_atmos.shape[:3], -1)  # (B, L, C_A, V_A*p*p)
+        atmos_preds = unpatchify(x_atmos, len(atmos_vars), H, W, self.patch_size)
 
         return Batch(
             {v: surf_preds[:, i] for i, v in enumerate(surf_vars)},

aurora/model/encoder.py

@@ -19,8 +19,6 @@
 from aurora.model.posencoding import pos_scale_enc
 from aurora.model.util import (
     check_lat_lon_dtype,
-    create_var_map,
-    get_ids_for_var_map,
     init_weights,
 )
 
@@ -78,8 +76,6 @@ def __init__(
 
         # We treat the static variables as surface variables in the model.
         surf_vars = surf_vars + static_vars if static_vars is not None else surf_vars
-        self.surf_var_map = create_var_map(surf_vars)
-        self.atmos_var_map = create_var_map(atmos_vars)
 
         # Latent tokens
         assert latent_levels > 1, "At least two latent levels are required."
@@ -102,10 +98,16 @@ def __init__(
         # Patch embeddings
         assert max_history_size > 0, "At least one history step is required."
         self.surf_token_embeds = LevelPatchEmbed(
-            len(surf_vars), patch_size, embed_dim, max_history_size
+            surf_vars,
+            patch_size,
+            embed_dim,
+            max_history_size,
         )
         self.atmos_token_embeds = LevelPatchEmbed(
-            len(atmos_vars), patch_size, embed_dim, max_history_size
+            atmos_vars,
+            patch_size,
+            embed_dim,
+            max_history_size,
         )
 
         # Learnable pressure level aggregation
@@ -194,14 +196,12 @@ def forward(self, batch: Batch, lead_time: timedelta) -> torch.Tensor:
 
         # Patch embed the surface level.
         x_surf = rearrange(x_surf, "b t v h w -> b v t h w")
-        surf_ids = get_ids_for_var_map(surf_vars, self.surf_var_map, x_surf.device)
-        x_surf = self.surf_token_embeds(x_surf, surf_ids)  # (B, L, D)
+        x_surf = self.surf_token_embeds(x_surf, surf_vars)  # (B, L, D)
         dtype = x_surf.dtype  # When using mixed precision, we need to keep track of the dtype.
 
         # Patch embed the atmospheric levels.
-        atmos_ids = get_ids_for_var_map(atmos_vars, self.atmos_var_map, x_atmos.device)
         x_atmos = rearrange(x_atmos, "b t v c h w -> (b c) v t h w")
-        x_atmos = self.atmos_token_embeds(x_atmos, atmos_ids)
+        x_atmos = self.atmos_token_embeds(x_atmos, atmos_vars)
         x_atmos = rearrange(x_atmos, "(b c) l d -> b c l d", b=B, c=C)
 
         # Add surface level encoding. This helps the model distinguish between surface and

aurora/model/patchembed.py

@@ -17,7 +17,7 @@ class LevelPatchEmbed(nn.Module):
 
     def __init__(
         self,
-        max_vars: int,
+        var_names: tuple[str, ...],
         patch_size: int,
         embed_dim: int,
         history_size: int = 1,
@@ -27,7 +27,7 @@ def __init__(
         """Initialise.
 
         Args:
-            max_vars (int): Maximum number of variables to embed.
+            var_names (tuple[str, ...]): Variables to embed.
             patch_size (int): Patch size.
             embed_dim (int): Embedding dimensionality.
             history_size (int, optional): Number of history dimensions. Defaults to `1`.
@@ -38,18 +38,19 @@ def __init__(
         """
         super().__init__()
 
-        self.max_vars = max_vars
+        self.var_names = var_names
         self.kernel_size = (history_size,) + to_2tuple(patch_size)
         self.flatten = flatten
         self.embed_dim = embed_dim
 
-        weight = torch.cat(
-            # Shape (C_out, C_in, T, H, W). `C_in = 1` here because we're embedding every variable
-            # separately.
-            [torch.empty(embed_dim, 1, *self.kernel_size) for _ in range(max_vars)],
-            dim=1,
+        self.weights = nn.ParameterDict(
+            {
+                # Shape (C_out, C_in, T, H, W). `C_in = 1` here because we're embedding every
+                # variable separately.
+                name: nn.Parameter(torch.empty(embed_dim, 1, *self.kernel_size))
+                for name in var_names
+            }
         )
-        self.weight = nn.Parameter(weight)
         self.bias = nn.Parameter(torch.empty(embed_dim))
         self.norm = norm_layer(embed_dim) if norm_layer else nn.Identity()
 
@@ -63,40 +64,47 @@ def init_weights(self) -> None:
         #
         #   https://github.com/pytorch/pytorch/issues/15314#issuecomment-477448573
         #
-        nn.init.kaiming_uniform_(self.weight, a=math.sqrt(5))
+        for weight in self.weights.values():
+            nn.init.kaiming_uniform_(weight, a=math.sqrt(5))
 
         # The following initialisation is taken from
         #
         #   https://pytorch.org/docs/stable/_modules/torch/nn/modules/conv.html#Conv3d
         #
-        fan_in, _ = nn.init._calculate_fan_in_and_fan_out(self.weight)
+        fan_in, _ = nn.init._calculate_fan_in_and_fan_out(next(iter(self.weights.values())))
         if fan_in != 0:
             bound = 1 / math.sqrt(fan_in)
             nn.init.uniform_(self.bias, -bound, bound)
 
-    def forward(self, x: torch.Tensor, var_ids: list[int]) -> torch.Tensor:
+    def forward(self, x: torch.Tensor, var_names: tuple[str, ...]) -> torch.Tensor:
         """Run the embedding.
 
         Args:
             x (:class:`torch.Tensor`): Tensor to embed of a shape of `(B, V, T, H, W)`.
-            var_ids (list[int]): A list of variable IDs. The length should be equal to `V`.
+            var_names (tuple[str, ...]): Names of the variables in `x`. The length should be equal
+                to `V`.
 
         Returns:
             :class:`torch.Tensor`: Embedded tensor a shape of `(B, L, D]) if flattened,
                 where `L = H * W / P^2`. Otherwise, the shape is `(B, D, H', W')`.
 
         """
         B, V, T, H, W = x.shape
-        assert len(var_ids) == V, f"{V} != {len(var_ids)}."
+        assert len(var_names) == V, f"{V} != {len(var_names)}."
         assert self.kernel_size[0] >= T, f"{T} > {self.kernel_size[0]}."
         assert H % self.kernel_size[1] == 0, f"{H} % {self.kernel_size[0]} != 0."
         assert W % self.kernel_size[2] == 0, f"{W} % {self.kernel_size[1]} != 0."
-        assert max(var_ids) < self.max_vars, f"{max(var_ids)} >= {self.max_vars}."
-        assert min(var_ids) >= 0, f"{min(var_ids)} < 0."
-        assert len(set(var_ids)) == len(var_ids), f"{var_ids} contains duplicates."
+        assert len(set(var_names)) == len(var_names), f"{var_names} contains duplicates."
 
         # Select the weights of the variables and history dimensions that are present in the batch.
-        weight = self.weight[:, var_ids, :T, ...]  # (C_out, C_in, T, H, W)
+        weight = torch.cat(
+            [
+                # (C_out, C_in, T, H, W)
+                self.weights[name][:, :, :T, ...]
+                for name in var_names
+            ],
+            dim=1,
+        )
         # Adjust the stride if history is smaller than maximum.
         stride = (T,) + self.kernel_size[1:]
 

aurora/model/util.py

@@ -9,8 +9,6 @@
 
 __all__ = [
     "unpatchify",
-    "create_var_map",
-    "get_ids_for_var_map",
     "check_lat_lon_dtype",
     "maybe_adjust_windows",
     "init_weights",
@@ -43,37 +41,6 @@ def unpatchify(x: torch.Tensor, V: int, H: int, W: int, P: int) -> torch.Tensor:
     return x
 
 
-def create_var_map(variables: tuple[str, ...]) -> dict[str, int]:
-    """Create dictionary where the keys are variable names and values are unique IDs.
-
-    Args:
-        variables (tuple[str, ...]): Variable strings.
-
-    Returns:
-        dict[str, int]: Variable map dictionary.
-    """
-    return {v: i for i, v in enumerate(variables)}
-
-
-def get_ids_for_var_map(
-    variables: tuple,
-    var_maps: dict,
-    device: torch.cuda.device,
-) -> torch.Tensor:
-    """Construct a tensor of variable IDs after retrieving those from a variable map created with
-    :func:`.create_var_map`.
-
-    Args:
-        variables (tuples[str, ...]): Variables to retrieve the IDs for.
-        var_maps (dict[str, int]): Variable map constructed with :func:`.create_var_map`.
-        device (torch.cuda.device): Device.
-
-    Returns:
-        torch.Tensor: Tensor of variable IDs found in `var_map`.
-    """
-    return torch.tensor([var_maps[v] for v in variables], device=device)
-
-
 def check_lat_lon_dtype(lat: torch.Tensor, lon: torch.Tensor) -> None:
     """Assert that `lat` and `lon` are at least `float32`s."""
     assert lat.dtype in [torch.float32, torch.float64], f"Latitude num. unstable: {lat.dtype}."

docs/beware.md

@@ -42,14 +42,3 @@ If you changed the model and added or removed parameters, you need to set `stric
 loading a checkpoint `Aurora.load_checkpoint(..., strict=False)`.
 Importantly, enabling or disabling LoRA for a model that was trained respectively without or
 with LoRA changes the parameters!
-
-## Extending the Model with New Surface-Level Variables
-
-Whereas we have attempted to design a robust and flexible model,
-inevitably some unfortunate design choices slipped through.
-
-A notable unfortunate design choice is that extending the model with a new surface-level
-variable breaks compatibility with existing checkpoints.
-It is possible to hack around this in a relatively simple way.
-We are working on a more principled fix.
-Please open an issue if this is a problem for you.