Source code for blackjax.mcmc.diffusions
# Copyright 2020- The Blackjax Authors.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
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"""Solvers for Langevin diffusions."""
from typing import NamedTuple
import jax
import jax.numpy as jnp
from blackjax.types import ArrayTree
from blackjax.util import generate_gaussian_noise
__all__ = ["overdamped_langevin"]
class DiffusionState(NamedTuple):
position: ArrayTree
logdensity: float
logdensity_grad: ArrayTree
[docs]
def overdamped_langevin(logdensity_grad_fn):
"""Euler solver for overdamped Langevin diffusion."""
def one_step(rng_key, state: DiffusionState, step_size: float, batch: tuple = ()):
position, _, logdensity_grad = state
noise = generate_gaussian_noise(rng_key, position)
position = jax.tree_util.tree_map(
lambda p, g, n: p + step_size * g + jnp.sqrt(2 * step_size) * n,
position,
logdensity_grad,
noise,
)
logdensity, logdensity_grad = logdensity_grad_fn(position, *batch)
return DiffusionState(position, logdensity, logdensity_grad)
return one_step