Upload scheduling_flow_matching.py

scheduling_flow_matching.py

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+from dataclasses import dataclass
+from typing import Optional, Tuple, Union, List
+import math
+import numpy as np
+import torch
+
+from diffusers.configuration_utils import ConfigMixin, register_to_config
+from diffusers.utils import BaseOutput, logging
+from diffusers.utils.torch_utils import randn_tensor
+from diffusers.schedulers.scheduling_utils import SchedulerMixin
+from IPython import embed
+
+
+@dataclass
+class FlowMatchEulerDiscreteSchedulerOutput(BaseOutput):
+    """
+    Output class for the scheduler's `step` function output.
+
+    Args:
+        prev_sample (`torch.FloatTensor` of shape `(batch_size, num_channels, height, width)` for images):
+            Computed sample `(x_{t-1})` of previous timestep. `prev_sample` should be used as next model input in the
+            denoising loop.
+    """
+
+    prev_sample: torch.FloatTensor
+
+
+class PyramidFlowMatchEulerDiscreteScheduler(SchedulerMixin, ConfigMixin):
+    """
+    Euler scheduler.
+
+    This model inherits from [`SchedulerMixin`] and [`ConfigMixin`]. Check the superclass documentation for the generic
+    methods the library implements for all schedulers such as loading and saving.
+
+    Args:
+        num_train_timesteps (`int`, defaults to 1000):
+            The number of diffusion steps to train the model.
+        timestep_spacing (`str`, defaults to `"linspace"`):
+            The way the timesteps should be scaled. Refer to Table 2 of the [Common Diffusion Noise Schedules and
+            Sample Steps are Flawed](https://huggingface.co/papers/2305.08891) for more information.
+        shift (`float`, defaults to 1.0):
+            The shift value for the timestep schedule.
+    """
+
+    _compatibles = []
+    order = 1
+
+    @register_to_config
+    def __init__(
+        self,
+        num_train_timesteps: int = 1000,
+        shift: float = 1.0,     # Following Stable diffusion 3, 
+        stages: int = 3,
+        stage_range: List = [0, 1/3, 2/3, 1],
+        gamma: float = 1/3,
+    ):
+        
+        self.timestep_ratios = {}           # The timestep ratio for each stage
+        self.timesteps_per_stage = {}       # The  detailed timesteps per stage
+        self.sigmas_per_stage = {}
+        self.start_sigmas = {}           
+        self.end_sigmas = {}
+        self.ori_start_sigmas = {}
+
+        # self.init_sigmas()
+        self.init_sigmas_for_each_stage()
+        self.sigma_min = self.sigmas[-1].item()
+        self.sigma_max = self.sigmas[0].item()
+        self.gamma = gamma
+
+    def init_sigmas(self):
+        """
+            initialize the global timesteps and sigmas
+        """
+        num_train_timesteps = self.config.num_train_timesteps
+        shift = self.config.shift
+
+        timesteps = np.linspace(1, num_train_timesteps, num_train_timesteps, dtype=np.float32)[::-1].copy()
+        timesteps = torch.from_numpy(timesteps).to(dtype=torch.float32)
+
+        sigmas = timesteps / num_train_timesteps
+        sigmas = shift * sigmas / (1 + (shift - 1) * sigmas)
+
+        self.timesteps = sigmas * num_train_timesteps
+
+        self._step_index = None
+        self._begin_index = None
+
+        self.sigmas = sigmas.to("cpu")  # to avoid too much CPU/GPU communication
+
+    def init_sigmas_for_each_stage(self):
+        """
+            Init the timesteps for each stage
+        """
+        self.init_sigmas()
+
+        stage_distance = []
+        stages = self.config.stages
+        training_steps = self.config.num_train_timesteps
+        stage_range = self.config.stage_range
+
+        # Init the start and end point of each stage
+        for i_s in range(stages):
+            # To decide the start and ends point
+            start_indice = int(stage_range[i_s] * training_steps)
+            start_indice = max(start_indice, 0)
+            end_indice = int(stage_range[i_s+1] * training_steps)
+            end_indice = min(end_indice, training_steps)
+            start_sigma = self.sigmas[start_indice].item()
+            end_sigma = self.sigmas[end_indice].item() if end_indice < training_steps else 0.0
+            self.ori_start_sigmas[i_s] = start_sigma
+
+            if i_s != 0:
+                ori_sigma = 1 - start_sigma
+                gamma = self.config.gamma
+                corrected_sigma = (1 / (math.sqrt(1 + (1 / gamma)) * (1 - ori_sigma) + ori_sigma)) * ori_sigma
+                # corrected_sigma = 1 / (2 - ori_sigma) * ori_sigma
+                start_sigma = 1 - corrected_sigma
+
+            stage_distance.append(start_sigma - end_sigma)
+            self.start_sigmas[i_s] = start_sigma
+            self.end_sigmas[i_s] = end_sigma
+
+        # Determine the ratio of each stage according to flow length
+        tot_distance = sum(stage_distance)
+        for i_s in range(stages):
+            if i_s == 0:
+                start_ratio = 0.0
+            else:
+                start_ratio = sum(stage_distance[:i_s]) / tot_distance
+            if i_s == stages - 1:
+                end_ratio = 1.0
+            else:
+                end_ratio = sum(stage_distance[:i_s+1]) / tot_distance
+
+            self.timestep_ratios[i_s] = (start_ratio, end_ratio)
+
+        # Determine the timesteps and sigmas for each stage
+        for i_s in range(stages):
+            timestep_ratio = self.timestep_ratios[i_s]
+            timestep_max = self.timesteps[int(timestep_ratio[0] * training_steps)]
+            timestep_min = self.timesteps[min(int(timestep_ratio[1] * training_steps), training_steps - 1)]
+            timesteps = np.linspace(
+                timestep_max, timestep_min, training_steps + 1,
+            )
+            self.timesteps_per_stage[i_s] = timesteps[:-1]
+            stage_sigmas = np.linspace(
+                1, 0, training_steps + 1,
+            )
+            self.sigmas_per_stage[i_s] = torch.from_numpy(stage_sigmas[:-1])
+
+    @property
+    def step_index(self):
+        """
+        The index counter for current timestep. It will increase 1 after each scheduler step.
+        """
+        return self._step_index
+
+    @property
+    def begin_index(self):
+        """
+        The index for the first timestep. It should be set from pipeline with `set_begin_index` method.
+        """
+        return self._begin_index
+
+    # Copied from diffusers.schedulers.scheduling_dpmsolver_multistep.DPMSolverMultistepScheduler.set_begin_index
+    def set_begin_index(self, begin_index: int = 0):
+        """
+        Sets the begin index for the scheduler. This function should be run from pipeline before the inference.
+
+        Args:
+            begin_index (`int`):
+                The begin index for the scheduler.
+        """
+        self._begin_index = begin_index
+
+    def _sigma_to_t(self, sigma):
+        return sigma * self.config.num_train_timesteps
+
+    def set_timesteps(self, num_inference_steps: int, stage_index: int, device: Union[str, torch.device] = None):
+        """
+            Setting the timesteps and sigmas for each stage 
+        """
+        self.num_inference_steps = num_inference_steps
+        training_steps = self.config.num_train_timesteps     
+        self.init_sigmas()
+
+        stage_timesteps = self.timesteps_per_stage[stage_index]
+        timestep_max = stage_timesteps[0].item()
+        timestep_min = stage_timesteps[-1].item()
+
+        timesteps = np.linspace(
+            timestep_max, timestep_min, num_inference_steps,
+        )
+        self.timesteps = torch.from_numpy(timesteps).to(device=device)
+
+        stage_sigmas = self.sigmas_per_stage[stage_index]
+        sigma_max = stage_sigmas[0].item()
+        sigma_min = stage_sigmas[-1].item()
+
+        ratios = np.linspace(
+            sigma_max, sigma_min, num_inference_steps
+        )
+        sigmas = torch.from_numpy(ratios).to(device=device)
+        self.sigmas = torch.cat([sigmas, torch.zeros(1, device=sigmas.device)])
+
+        self._step_index = None
+
+    def index_for_timestep(self, timestep, schedule_timesteps=None):
+        if schedule_timesteps is None:
+            schedule_timesteps = self.timesteps
+
+        indices = (schedule_timesteps == timestep).nonzero()
+
+        # The sigma index that is taken for the **very** first `step`
+        # is always the second index (or the last index if there is only 1)
+        # This way we can ensure we don't accidentally skip a sigma in
+        # case we start in the middle of the denoising schedule (e.g. for image-to-image)
+        pos = 1 if len(indices) > 1 else 0
+
+        return indices[pos].item()
+
+    def _init_step_index(self, timestep):
+        if self.begin_index is None:
+            if isinstance(timestep, torch.Tensor):
+                timestep = timestep.to(self.timesteps.device)
+            self._step_index = self.index_for_timestep(timestep)
+        else:
+            self._step_index = self._begin_index
+
+    def step(
+        self,
+        model_output: torch.FloatTensor,
+        timestep: Union[float, torch.FloatTensor],
+        sample: torch.FloatTensor,
+        generator: Optional[torch.Generator] = None,
+        return_dict: bool = True,
+    ) -> Union[FlowMatchEulerDiscreteSchedulerOutput, Tuple]:
+        """
+        Predict the sample from the previous timestep by reversing the SDE. This function propagates the diffusion
+        process from the learned model outputs (most often the predicted noise).
+
+        Args:
+            model_output (`torch.FloatTensor`):
+                The direct output from learned diffusion model.
+            timestep (`float`):
+                The current discrete timestep in the diffusion chain.
+            sample (`torch.FloatTensor`):
+                A current instance of a sample created by the diffusion process.
+            generator (`torch.Generator`, *optional*):
+                A random number generator.
+            return_dict (`bool`):
+                Whether or not to return a [`~schedulers.scheduling_euler_discrete.EulerDiscreteSchedulerOutput`] or
+                tuple.
+
+        Returns:
+            [`~schedulers.scheduling_euler_discrete.EulerDiscreteSchedulerOutput`] or `tuple`:
+                If return_dict is `True`, [`~schedulers.scheduling_euler_discrete.EulerDiscreteSchedulerOutput`] is
+                returned, otherwise a tuple is returned where the first element is the sample tensor.
+        """
+
+        if (
+            isinstance(timestep, int)
+            or isinstance(timestep, torch.IntTensor)
+            or isinstance(timestep, torch.LongTensor)
+        ):
+            raise ValueError(
+                (
+                    "Passing integer indices (e.g. from `enumerate(timesteps)`) as timesteps to"
+                    " `EulerDiscreteScheduler.step()` is not supported. Make sure to pass"
+                    " one of the `scheduler.timesteps` as a timestep."
+                ),
+            )
+
+        if self.step_index is None:
+            self._step_index = 0
+
+        # Upcast to avoid precision issues when computing prev_sample
+        sample = sample.to(torch.float32)
+
+        sigma = self.sigmas[self.step_index]
+        sigma_next = self.sigmas[self.step_index + 1]
+
+        prev_sample = sample + (sigma_next - sigma) * model_output
+
+        # Cast sample back to model compatible dtype
+        prev_sample = prev_sample.to(model_output.dtype)
+
+        # upon completion increase step index by one
+        self._step_index += 1
+
+        if not return_dict:
+            return (prev_sample,)
+
+        return FlowMatchEulerDiscreteSchedulerOutput(prev_sample=prev_sample)
+
+    def __len__(self):
+        return self.config.num_train_timesteps