flax.linen.while_loop(cond_fn, body_fn, mdl, init, carry_variables=False, broadcast_variables=True, split_rngs=FrozenDict({}))[source]#

Lifted version of jax.lax.while_loop.

The lifted scope is passed to cond_fn and body_fn. Broadcasted variables are immutable. The carry variable are mutable but cannot change shape and dtype. This also means you cannot initialize variables inside the body. Consider calling body_fn once manually before calling while_loop if variable initialization is required.


>>> import flax.linen as nn
>>> import jax, jax.numpy as jnp

>>> class WhileLoopExample(nn.Module):
...   @nn.compact
...   def __call__(self, x):
...     def cond_fn(mdl, c):
...       return mdl.variables['state']['acc'] < 10
...     def body_fn(mdl, c):
...       acc = mdl.variable('state', 'acc', lambda: jnp.array(0))
...       acc.value += 1
...       y = nn.Dense(c.shape[-1])(c)
...       return y
...     c = x
...     if self.is_mutable_collection('params'):
...       return body_fn(self, c)
...     else:
...       return nn.while_loop(cond_fn, body_fn, self, c,
...                             carry_variables='state')

>>> k = jax.random.key(0)
>>> x = jnp.ones((2, 2))
>>> intial_vars = WhileLoopExample().init(k, x)
>>> result, state = WhileLoopExample().apply(intial_vars, x, mutable=['state'])
  • cond_fn – Should return True as long as the loop should continue.

  • body_fn – The body of the while loop.

  • mdl – The Module which should be lifted into the loop.

  • init – The initial state passed to the loop

  • carry_variables – collections that are carried through the loop and are therefore mutable (default: none).

  • broadcast_variables – collections that are closed over and are therefore read-only (default: all collections)

  • split_rngs – Split PRNG sequences will be different for each loop iterations. If split is False the PRNGs will be the same across iterations.


The final state after executing the while loop.