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src/diffusion/flow_matching/training_pyramid.py

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+import torch
+from typing import Callable
+from src.diffusion.base.training import *
+from src.diffusion.base.scheduling import BaseScheduler
+
+def inverse_sigma(alpha, sigma):
+    return 1/sigma**2
+def snr(alpha, sigma):
+    return alpha/sigma
+def minsnr(alpha, sigma, threshold=5):
+    return torch.clip(alpha/sigma, min=threshold)
+def maxsnr(alpha, sigma, threshold=5):
+    return torch.clip(alpha/sigma, max=threshold)
+def constant(alpha, sigma):
+    return 1
+
+class PyramidTrainer(BaseTrainer):
+    def __init__(
+            self,
+            scheduler: BaseScheduler,
+            loss_weight_fn:Callable=constant,
+            lognorm_t=False,
+            *args,
+            **kwargs
+    ):
+        super().__init__(*args, **kwargs)
+        self.lognorm_t = lognorm_t
+        self.scheduler = scheduler
+        self.loss_weight_fn = loss_weight_fn
+
+
+    def _impl_trainstep(self, net, ema_net, raw_images, x, y):
+        batch_size = x.shape[0]
+        if self.lognorm_t:
+            t = torch.randn(batch_size).to(x.device, x.dtype).sigmoid()
+        else:
+            t = torch.rand(batch_size).to(x.device, x.dtype)
+        noise = torch.randn_like(x)
+        alpha = self.scheduler.alpha(t)
+        dalpha = self.scheduler.dalpha(t)
+        sigma = self.scheduler.sigma(t)
+        dsigma = self.scheduler.dsigma(t)
+        w = self.scheduler.w(t)
+
+        x_t = alpha * x + noise * sigma
+        v_t = dalpha * x + dsigma * noise
+
+
+        output_pyramid = []
+        def feature_hook(module, input, output):
+           output_pyramid.extend(output)
+        handle = net.decoder.register_forward_hook(feature_hook)
+        net(x_t, t, y)
+        handle.remove()
+
+        loss = 0.0
+        out_dict = dict()
+
+        cur_v_t = v_t
+        for i in range(len(output_pyramid)):
+            cur_out = output_pyramid[i]
+            loss_i = (cur_v_t - cur_out) ** 2
+            loss += loss_i.mean()
+            out_dict["loss_{}".format(i)] = loss_i.mean()
+            cur_v_t = torch.nn.functional.interpolate(cur_v_t, scale_factor=0.5, mode='bilinear', align_corners=False)
+        out_dict["loss"] = loss
+        return out_dict
+