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Running
on
Zero
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# // Copyright (c) 2025 Bytedance Ltd. and/or its affiliates
# //
# // 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.
"""
Type definitions.
"""
from enum import Enum
class PredictionType(str, Enum):
"""
x_0:
Predict data sample.
x_T:
Predict noise sample.
Proposed by DDPM (https://arxiv.org/abs/2006.11239)
Proved problematic by zsnr paper (https://arxiv.org/abs/2305.08891)
v_cos:
Predict velocity dx/dt based on the cosine schedule (A_t * x_T - B_t * x_0).
Proposed by progressive distillation (https://arxiv.org/abs/2202.00512)
v_lerp:
Predict velocity dx/dt based on the lerp schedule (x_T - x_0).
Proposed by rectified flow (https://arxiv.org/abs/2209.03003)
"""
x_0 = "x_0"
x_T = "x_T"
v_cos = "v_cos"
v_lerp = "v_lerp"
class SamplingDirection(str, Enum):
"""
backward: Sample from x_T to x_0 for data generation.
forward: Sample from x_0 to x_T for noise inversion.
"""
backward = "backward"
forward = "forward"
@staticmethod
def reverse(direction):
if direction == SamplingDirection.backward:
return SamplingDirection.forward
if direction == SamplingDirection.forward:
return SamplingDirection.backward
raise NotImplementedError
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