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# Copyright 2022 The HuggingFace Team. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import math
import flax.linen as nn
import jax.numpy as jnp
def get_sinusoidal_embeddings(
timesteps: jnp.ndarray,
embedding_dim: int,
freq_shift: float = 1,
min_timescale: float = 1,
max_timescale: float = 1.0e4,
flip_sin_to_cos: bool = False,
scale: float = 1.0,
) -> jnp.ndarray:
"""Returns the positional encoding (same as Tensor2Tensor).
Args:
timesteps: a 1-D Tensor of N indices, one per batch element.
These may be fractional.
embedding_dim: The number of output channels.
min_timescale: The smallest time unit (should probably be 0.0).
max_timescale: The largest time unit.
Returns:
a Tensor of timing signals [N, num_channels]
"""
assert timesteps.ndim == 1, "Timesteps should be a 1d-array"
assert embedding_dim % 2 == 0, f"Embedding dimension {embedding_dim} should be even"
num_timescales = float(embedding_dim // 2)
log_timescale_increment = math.log(max_timescale / min_timescale) / (num_timescales - freq_shift)
inv_timescales = min_timescale * jnp.exp(jnp.arange(num_timescales, dtype=jnp.float32) * -log_timescale_increment)
emb = jnp.expand_dims(timesteps, 1) * jnp.expand_dims(inv_timescales, 0)
# scale embeddings
scaled_time = scale * emb
if flip_sin_to_cos:
signal = jnp.concatenate([jnp.cos(scaled_time), jnp.sin(scaled_time)], axis=1)
else:
signal = jnp.concatenate([jnp.sin(scaled_time), jnp.cos(scaled_time)], axis=1)
signal = jnp.reshape(signal, [jnp.shape(timesteps)[0], embedding_dim])
return signal
class FlaxTimestepEmbedding(nn.Module):
r"""
Time step Embedding Module. Learns embeddings for input time steps.
Args:
time_embed_dim (`int`, *optional*, defaults to `32`):
Time step embedding dimension
dtype (:obj:`jnp.dtype`, *optional*, defaults to jnp.float32):
Parameters `dtype`
"""
time_embed_dim: int = 32
dtype: jnp.dtype = jnp.float32
@nn.compact
def __call__(self, temb):
temb = nn.Dense(self.time_embed_dim, dtype=self.dtype, name="linear_1")(temb)
temb = nn.silu(temb)
temb = nn.Dense(self.time_embed_dim, dtype=self.dtype, name="linear_2")(temb)
return temb
class FlaxTimesteps(nn.Module):
r"""
Wrapper Module for sinusoidal Time step Embeddings as described in https://arxiv.org/abs/2006.11239
Args:
dim (`int`, *optional*, defaults to `32`):
Time step embedding dimension
"""
dim: int = 32
flip_sin_to_cos: bool = False
freq_shift: float = 1
@nn.compact
def __call__(self, timesteps):
return get_sinusoidal_embeddings(
timesteps, embedding_dim=self.dim, flip_sin_to_cos=self.flip_sin_to_cos, freq_shift=self.freq_shift
)
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