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# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
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#     http://www.apache.org/licenses/LICENSE-2.0
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"""Helper functions for GRPO Trainer."""

import jax


def compute_advantages(rewards: jax.Array, num_generations: int) -> jax.Array:
  """Compute group relative advantages.

  Args:
    rewards: reward functions output.
    num_generations: Number of generations.

  Returns:
    Group relative advantages.
  """
  mean_grouped_rewards = rewards.reshape(-1, num_generations).mean(axis=1)
  std_grouped_rewards = rewards.reshape(-1, num_generations).std(axis=1, ddof=1)

  mean_grouped_rewards = mean_grouped_rewards.repeat(num_generations)
  std_grouped_rewards = std_grouped_rewards.repeat(num_generations)
  return (rewards - mean_grouped_rewards) / (std_grouped_rewards + 1e-4)
