Merge pull request #9 from neonbjb:causal

Add causal timestep adjustments

codes/models/diffusion/gaussian_diffusion.py

@@ -17,6 +17,63 @@ from .nn import mean_flat
 from .losses import normal_kl, discretized_gaussian_log_likelihood
 
 
+def causal_timestep_adjustment(t, S, num_timesteps, causal_slope=1, add_jitter=True):
+    """
+    Remaps [t] from a batch of integers into a causal sequence [S] long where each sequence element is [causal_slope]
+    timesteps advanced from the previous sequence element. At t=0, the sequence is all 0s and at t=[num_timesteps], the
+    sequence is all [num_timesteps].
+
+    As a result of the last property, longer sequences will have larger "gaps" between them in continuous space. This must
+    be considered at inference time.
+    :param t: Batched timestep integers
+    :param S: Sequence length.
+    :param num_timesteps: Number of total timesteps.
+    :param causal_slope: The causal slope. Ex: "2" means each sequence element will be 2 timesteps ahead of its predecessor.
+    :param add_jitter: Whether or not to add random jitter into the extra gaps between timesteps added by this function.
+                       Should be true for training and false for inference.
+    :return: [b,S] sequence of timestep integers.
+    """
+    S_sloped = causal_slope * (S-1)
+    # This algorithm for adding causality does so by simply adding S_sloped additional timesteps. To make this
+    # actually work, we map the existing t from the timescale specified to the model to the causal timescale:
+    adj_t = t * (num_timesteps + S_sloped) // num_timesteps
+    if add_jitter:
+        jitter = (random.random() - .5) * S_sloped
+        adj_t = (adj_t+jitter).clamp(0, num_timesteps+S_sloped)
+
+    # Now use the re-mapped adj_t to create a timestep vector that propagates across the sequence with the specified slope.
+    t = adj_t.unsqueeze(1).repeat(1, S)
+    t = (t - torch.arange(0, S) * causal_slope).clamp(0, num_timesteps).long()
+    return t
+
+
+def graph_causal_timestep_adjustment():
+    S = 400
+    slope=4
+    num_timesteps=4000
+    #for num_timesteps in range(100, 4000, 200):
+    t_res = []
+    for t in range(num_timesteps, -1, -num_timesteps//50):
+        T = causal_timestep_adjustment(torch.tensor([t]), S, num_timesteps, causal_slope=slope, add_jitter=False)[0]
+        t_res.append(T)
+        plt.plot(T.numpy())
+        plt.ylim(0,4000)
+        plt.xlim(0,500)
+        plt.savefig(f'{t}.png')
+        plt.clf()
+
+    for i in range(len(t_res)):
+        for j in range(len(t_res)):
+            if i == j:
+                continue
+            #assert not torch.all(t_res[i] == t_res[j])
+    plt.ylim(0,4000)
+    plt.xlim(0,500)
+    plt.ylabel('timestep')
+    plt.savefig(f'{num_timesteps}.png')
+    plt.clf()
+
+
 def get_named_beta_schedule(schedule_name, num_diffusion_timesteps):
     """
     Get a pre-defined beta schedule for the given name.
@@ -790,6 +847,14 @@ class GaussianDiffusion:
         output = th.where((t == 0).view(-1, 1, 1), decoder_nll, kl)
         return {"output": output, "pred_xstart": out["pred_xstart"]}
 
+    def causal_training_losses(self, model, x_start, t, causal_slope=1, model_kwargs=None, noise=None, channel_balancing_fn=None):
+        """
+        Compute training losses for a causal diffusion process.
+        """
+        assert len(x_start.shape) == 3, "causal_training_losses assumes a 1d sequence with the axis being the time axis."
+        t = causal_timestep_adjustment(t, x_start.shape[-1], self.num_timesteps, causal_slope, add_jitter=True)
+        return self.training_losses(model, x_start, t, model_kwargs, noise, channel_balancing_fn)
+
     def training_losses(self, model, x_start, t, model_kwargs=None, noise=None, channel_balancing_fn=None):
         """
         Compute training losses for a single timestep.