update flax scheduler API (#822)

* update flax scheduler API

* remoev set format

* fix call to scale_model_input

* update flax pndm

* use int32

* update docstr

src/diffusers/pipelines/stable_diffusion/pipeline_flax_stable_diffusion.py

@@ -170,6 +170,8 @@ class FlaxStableDiffusionPipeline(FlaxDiffusionPipeline):
             t = jnp.array(scheduler_state.timesteps, dtype=jnp.int32)[step]
             timestep = jnp.broadcast_to(t, latents_input.shape[0])
 
+            latents_input = self.scheduler.scale_model_input(scheduler_state, latents_input, t)
+
             # predict the noise residual
             noise_pred = self.unet.apply(
                 {"params": params["unet"]},
@@ -189,6 +191,9 @@ class FlaxStableDiffusionPipeline(FlaxDiffusionPipeline):
             params["scheduler"], num_inference_steps=num_inference_steps, shape=latents.shape
         )
 
+        # scale the initial noise by the standard deviation required by the scheduler
+        latents = latents * self.scheduler.init_noise_sigma
+
         if debug:
             # run with python for loop
             for i in range(num_inference_steps):

src/diffusers/schedulers/scheduling_ddim_flax.py

@@ -141,6 +141,23 @@ class FlaxDDIMScheduler(FlaxSchedulerMixin, ConfigMixin):
         # whether we use the final alpha of the "non-previous" one.
         self.final_alpha_cumprod = jnp.array(1.0) if set_alpha_to_one else float(self._alphas_cumprod[0])
 
+        # standard deviation of the initial noise distribution
+        self.init_noise_sigma = 1.0
+
+    def scale_model_input(
+        self, state: DDIMSchedulerState, sample: jnp.ndarray, timestep: Optional[int] = None
+    ) -> jnp.ndarray:
+        """
+        Args:
+            state (`PNDMSchedulerState`): the `FlaxPNDMScheduler` state data class instance.
+            sample (`jnp.ndarray`): input sample
+            timestep (`int`, optional): current timestep
+
+        Returns:
+            `jnp.ndarray`: scaled input sample
+        """
+        return sample
+
     def create_state(self):
         return DDIMSchedulerState.create(
             num_train_timesteps=self.config.num_train_timesteps, alphas_cumprod=self._alphas_cumprod

src/diffusers/schedulers/scheduling_pndm_flax.py

@@ -153,6 +153,9 @@ class FlaxPNDMScheduler(FlaxSchedulerMixin, ConfigMixin):
         # mainly at formula (9), (12), (13) and the Algorithm 2.
         self.pndm_order = 4
 
+        # standard deviation of the initial noise distribution
+        self.init_noise_sigma = 1.0
+
     def create_state(self):
         return PNDMSchedulerState.create(num_train_timesteps=self.config.num_train_timesteps)
 
@@ -196,7 +199,7 @@ class FlaxPNDMScheduler(FlaxSchedulerMixin, ConfigMixin):
             )
 
         return state.replace(
-            timesteps=jnp.concatenate([state.prk_timesteps, state.plms_timesteps]).astype(jnp.int64),
+            timesteps=jnp.concatenate([state.prk_timesteps, state.plms_timesteps]).astype(jnp.int32),
             counter=0,
             # Reserve space for the state variables
             cur_model_output=jnp.zeros(shape),
@@ -204,6 +207,23 @@ class FlaxPNDMScheduler(FlaxSchedulerMixin, ConfigMixin):
             ets=jnp.zeros((4,) + shape),
         )
 
+    def scale_model_input(
+        self, state: PNDMSchedulerState, sample: jnp.ndarray, timestep: Optional[int] = None
+    ) -> jnp.ndarray:
+        """
+        Ensures interchangeability with schedulers that need to scale the denoising model input depending on the
+        current timestep.
+
+        Args:
+            state (`PNDMSchedulerState`): the `FlaxPNDMScheduler` state data class instance.
+            sample (`jnp.ndarray`): input sample
+            timestep (`int`, optional): current timestep
+
+        Returns:
+            `jnp.ndarray`: scaled input sample
+        """
+        return sample
+
     def step(
         self,
         state: PNDMSchedulerState,