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[MAX] Add shift_terminal support for Qwen-Image #7

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[MAX] Add shift_terminal support for Qwen-Image #7

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5f30022
Add shift_terminal support to FlowMatchEulerDiscreteScheduler
jglee-sqbits Mar 10, 2026
ba87ec6
Format flow match scheduler
jglee-sqbits Mar 11, 2026
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12 changes: 12 additions & 0 deletions max/python/max/pipelines/lib/diffusion_schedulers/scheduling_flow_match_euler_discrete.py
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,7 @@ def __init__(
use_flow_sigmas: bool = False,
use_dynamic_shifting: bool = False,
use_empirical_mu: bool = False,
shift_terminal: float | None = None,
order: int = 1,
**unused_kwargs,
) -> None:
Expand All @@ -46,6 +47,8 @@ def __init__(
use_flow_sigmas: Whether to use flow sigmas.
use_dynamic_shifting: Whether to use dynamic shifting.
use_empirical_mu: Whether to use empirical mu.
shift_terminal: If set, stretch shifted sigmas so the last
sigma equals this value instead of 1/num_steps.
order: Order of the scheduler.
**unused_kwargs: Unused keyword arguments.
"""
Expand All @@ -56,6 +59,7 @@ def __init__(
self.use_flow_sigmas = use_flow_sigmas
self.use_dynamic_shifting = use_dynamic_shifting
self.use_empirical_mu = use_empirical_mu
self.shift_terminal = shift_terminal
self.order = order

self._use_flow_sigmas = use_flow_sigmas
Expand Down Expand Up @@ -145,6 +149,14 @@ def retrieve_timesteps_and_sigmas(
if self._use_dynamic_shifting:
mu = self._calculate_mu(image_seq_len, num_inference_steps)
sigmas = self._time_shift_exponential(mu, 1.0, sigmas)

# Stretch sigmas so the last value equals shift_terminal
# (matches diffusers stretch_shift_to_terminal)
if self.shift_terminal is not None and self.shift_terminal > 0:
one_minus_z = 1.0 - sigmas
scale_factor = one_minus_z[-1] / (1.0 - self.shift_terminal)
sigmas = (1.0 - (one_minus_z / scale_factor)).astype(np.float32)

timesteps = sigmas * 1000.0
if reverse:
timesteps = ((1000.0 - timesteps) / 1000.0).astype(np.float32)
Expand Down
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