SMC: Joint tuning and pretuning

blackjax/smc/inner_kernel_tuning.py

@@ -1,5 +1,7 @@
 from typing import Callable, Dict, NamedTuple, Tuple
 
+import jax
+
 from blackjax.base import SamplingAlgorithm
 from blackjax.smc.base import SMCInfo, SMCState
 from blackjax.types import ArrayTree, PRNGKey
@@ -28,8 +30,11 @@ def build_kernel(
     mcmc_step_fn: Callable,
     mcmc_init_fn: Callable,
     resampling_fn: Callable,
-    mcmc_parameter_update_fn: Callable[[SMCState, SMCInfo], Dict[str, ArrayTree]],
+    mcmc_parameter_update_fn: Callable[
+        [PRNGKey, SMCState, SMCInfo], Dict[str, ArrayTree]
+    ],
     num_mcmc_steps: int = 10,
+    smc_returns_state_with_parameter_override=False,
     **extra_parameters,
 ) -> Callable:
     """In the context of an SMC sampler (whose step_fn returning state has a .particles attribute), there's an inner
@@ -40,7 +45,8 @@ def build_kernel(
     ----------
     smc_algorithm
         Either blackjax.adaptive_tempered_smc or blackjax.tempered_smc (or any other implementation of
-        a sampling algorithm that returns an SMCState and SMCInfo pair).
+        a sampling algorithm that returns an SMCState and SMCInfo pair). It is also possible for this
+        to return an StateWithParameterOverride, in such case smc_returns_state_with_parameter_override needs to be True
     logprior_fn
         A function that computes the log density of the prior distribution
     loglikelihood_fn
@@ -54,7 +60,30 @@ def build_kernel(
         A callable that takes the SMCState and SMCInfo at step i and constructs a parameter to be used by the inner kernel in i+1 iteration.
     extra_parameters:
         parameters to be used for the creation of the smc_algorithm.
+    smc_returns_state_with_parameter_override:
+        a boolean indicating that the underlying smc_algorithm returns a smc_returns_state_with_parameter_override.
+        this is used in order to compose different adaptation mechanisms, such as pretuning with tuning.
     """
+    if smc_returns_state_with_parameter_override:
+
+        def extract_state_for_delegate(state):
+            return state
+
+        def compose_new_state(new_state, new_parameter_override):
+            composed_parameter_override = (
+                new_state.parameter_override | new_parameter_override
+            )
+            return StateWithParameterOverride(
+                new_state.sampler_state, composed_parameter_override
+            )
+
+    else:
+
+        def extract_state_for_delegate(state):
+            return state.sampler_state
+
+        def compose_new_state(new_state, new_parameter_override):
+            return StateWithParameterOverride(new_state, new_parameter_override)
 
     def kernel(
         rng_key: PRNGKey, state: StateWithParameterOverride, **extra_step_parameters
@@ -69,9 +98,14 @@ def kernel(
             num_mcmc_steps=num_mcmc_steps,
             **extra_parameters,
         ).step
-        new_state, info = step_fn(rng_key, state.sampler_state, **extra_step_parameters)
-        new_parameter_override = mcmc_parameter_update_fn(new_state, info)
-        return StateWithParameterOverride(new_state, new_parameter_override), info
+        parameter_update_key, step_key = jax.random.split(rng_key, 2)
+        new_state, info = step_fn(
+            step_key, extract_state_for_delegate(state), **extra_step_parameters
+        )
+        new_parameter_override = mcmc_parameter_update_fn(
+            parameter_update_key, new_state, info
+        )
+        return compose_new_state(new_state, new_parameter_override), info
 
     return kernel
 
@@ -83,9 +117,12 @@ def as_top_level_api(
     mcmc_step_fn: Callable,
     mcmc_init_fn: Callable,
     resampling_fn: Callable,
-    mcmc_parameter_update_fn: Callable[[SMCState, SMCInfo], Dict[str, ArrayTree]],
+    mcmc_parameter_update_fn: Callable[
+        [PRNGKey, SMCState, SMCInfo], Dict[str, ArrayTree]
+    ],
     initial_parameter_value,
     num_mcmc_steps: int = 10,
+    smc_returns_state_with_parameter_override=False,
     **extra_parameters,
 ) -> SamplingAlgorithm:
     """In the context of an SMC sampler (whose step_fn returning state
@@ -130,6 +167,7 @@ def as_top_level_api(
         resampling_fn,
         mcmc_parameter_update_fn,
         num_mcmc_steps,
+        smc_returns_state_with_parameter_override,
         **extra_parameters,
     )
 

blackjax/smc/pretuning.py

@@ -99,15 +99,21 @@ def update_parameter_distribution(
     )
 
 
+def default_measure_factory(state):
+    inverse_mass_matrix = state.parameter_override["inverse_mass_matrix"]
+    if not (len(inverse_mass_matrix.shape) == 3 and inverse_mass_matrix.shape[0] == 1):
+        raise ValueError("ESJD only works if chains share the inverse_mass_matrix.")
+
+    return esjd(inverse_mass_matrix[0])
+
+
 def build_pretune(
     mcmc_init_fn: Callable,
     mcmc_step_fn: Callable,
     alpha: float,
     sigma_parameters: ArrayLikeTree,
     n_particles: int,
-    performance_of_chain_measure_factory: Callable = lambda state: esjd(
-        state.parameter_override["inverse_mass_matrix"]
-    ),
+    performance_of_chain_measure_factory: Callable = default_measure_factory,
     natural_parameters: Optional[List[str]] = None,
     positive_parameters: Optional[List[str]] = None,
 ):

blackjax/smc/tuning/from_particles.py

@@ -12,7 +12,7 @@
     "particles_means",
     "particles_stds",
     "particles_covariance_matrix",
-    "mass_matrix_from_particles",
+    "inverse_mass_matrix_from_particles",
 ]
 
 
@@ -28,18 +28,16 @@ def particles_covariance_matrix(particles):
     return jnp.cov(particles_as_rows(particles), ddof=0, rowvar=False)
 
 
-def mass_matrix_from_particles(particles) -> Array:
+def inverse_mass_matrix_from_particles(particles) -> Array:
     """
     Implements tuning from section 3.1 from https://arxiv.org/pdf/1808.07730.pdf
-    Computing a mass matrix to be used in HMC from particles.
-    Given the particles covariance matrix, set all non-diagonal elements as zero,
-    take the inverse, and keep the diagonal.
+    Computing an inverse mass matrix to be used in HMC from particles.
 
     Returns
     -------
-    A mass Matrix
+    An inverse mass matrix
     """
-    return jnp.diag(1.0 / jnp.var(particles_as_rows(particles), axis=0))
+    return jnp.diag(jnp.var(particles_as_rows(particles), axis=0))
 
 
 def particles_as_rows(particles):