Add pointer to proof that CyclicPoissonSampling's procedure is equivalent to Poisson sampling.

PiperOrigin-RevId: 861797572

Author: arung54

jax_privacy/batch_selection.py

@@ -248,6 +248,8 @@ def batch_iterator(
 
     for i in range(self.iterations):
       current_group = partition[i % self.cycle_length]
+      # See Lemma 1 of https://arxiv.org/abs/2406.17298v3 for a proof this
+      # is equivalent to Poisson sampling.
       sample_size = rng.binomial(n=len(current_group), p=self.sampling_prob)
       if self.truncated_batch_size is not None:
         sample_size = min(sample_size, self.truncated_batch_size)