Fix: Configure gradient accumulation and chunking collator for stable training

[quangkmhd]

Summary

This PR updates the training configuration to enable gradient accumulation. This change stabilizes the training loss and prevents the ValueError: matrix contains invalid numeric entries error, which often occurs due to unstable gradients when training with small batch sizes.

Changes

• Modified sam3/train/configs/roboflow_v100/roboflow_v100_full_ft_100_images.yaml:
  • Increased gradient_accumulation_steps to 16.
  • Increased train_batch_size to 16.
  • Switched collate_fn to sam3.train.data.collator.collate_fn_api_with_chunking. This is critical because the trainer expects a list of micro-batches (chunks) when gradient accumulation is enabled, whereas the original collate_fn_api returned a single batch dict, causing an AssertionError.
  • Added the num_chunks parameter linked to gradient_accumulation_steps.

Verified

Tested locally. The training process is now stable, and the ValueError regarding invalid numeric entries in the cost matrix is resolved.

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