fix: update flow matching loss and variable names

lumina_train.py

@@ -294,7 +294,7 @@ def train(args):
     # load lumina
     nextdit = lumina_util.load_lumina_model(
         args.pretrained_model_name_or_path,
-        loading_dtype,
+        weight_dtype,
         torch.device("cpu"),
         disable_mmap=args.disable_mmap_load_safetensors,
         use_flash_attn=args.use_flash_attn,
@@ -494,6 +494,8 @@ def train(args):
 
     clean_memory_on_device(accelerator.device)
 
+    is_swapping_blocks = args.blocks_to_swap is not None and args.blocks_to_swap > 0
+
     if args.deepspeed:
         ds_model = deepspeed_utils.prepare_deepspeed_model(args, nextdit=nextdit)
         # most of ZeRO stage uses optimizer partitioning, so we have to prepare optimizer and ds_model at the same time. # pull/1139#issuecomment-1986790007
@@ -739,7 +741,7 @@ def train(args):
                 with accelerator.autocast():
                     # YiYi notes: divide it by 1000 for now because we scale it by 1000 in the transformer model (we should not keep it but I want to keep the inputs same for the model for testing)
                     model_pred = nextdit(
-                        x=img,  # image latents (B, C, H, W)
+                        x=noisy_model_input,  # image latents (B, C, H, W)
                         t=timesteps / 1000,  # timesteps需要除以1000来匹配模型预期
                         cap_feats=gemma2_hidden_states,  # Gemma2的hidden states作为caption features
                         cap_mask=gemma2_attn_mask.to(
@@ -751,8 +753,8 @@ def train(args):
                     args, model_pred, noisy_model_input, sigmas
                 )
 
-                # flow matching loss: this is different from SD3
-                target = noise - latents
+                # flow matching loss
+                target = latents - noise
 
                 # calculate loss
                 huber_c = train_util.get_huber_threshold_if_needed(