DPMSolverMultistepScheduler, how to correctly denoise the specific noise step ?

[HuangChiEn]

I'm trying to add the small noise (step t=1) on the latent. Although the document doesn't cover how to add the noise to it, but I found a method called add_noise, which seems fit to my requirements.

(I have looked DPM-solver++ paper, and the add_noise works exactly match with Eq.1, so I think it can be used to add noise to it).

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The issue I faced is that I have no idea how to denoise the noise latent by calling the scheduler.step(.) method.
The following image shows the way I had tried :

sample_latent is the ground truth (GT), while I calculate the difference between the noise latent with the GT. Then no surprised, the 49-th step noise is the latent with less noise, and i take it as my noise latent.

This is how I call the step method :
apprx_latent = self.scheduler.step(noise, t, noise_latent, **extra_step_kwargs, return_dict=False)[0] , where t=timesteps[0].

Yeah, I have noticed that it should be t=timesteps[49] to consist with the timestep index of noise latent. However, let t=timesteps[-1] (which is 49-th step) have the worse results, so I think the first time step is correct.

Unfortunately, the noise latent seems closer to the GT comparing with the denoised latent..

Any suggestion will be appreciated!!