sequince.density

Callable-based sequential and tempered target densities.

Classes

SequentialDensity	Sequential target defined by density and increment callables.
TemperedDensity	Tempered target defined by an initial density and a log-density ratio.

Module Contents

class sequince.density.SequentialDensity(log_prob, log_increment, *, evaluation_key=None)

Bases: _DensityComponents, sequince.target.SequentialTarget

Sequential target defined by density and increment callables.

log_prob returns the current target log density for MCMC; log_increment returns the complete weight increment. Both accept particles and optionally context. Weighting calls only the increment. MCMC evaluates and caches log_prob separately.

For context-dependent densities, supply evaluation_key(context) to identify the stage relevant to cached density values, or explicitly refresh the evaluation when the density changes. Keys must be hashable; compiled execution requires static keys.

Parameters:

• log_prob (sequince.target.TargetComponentFn)

• log_increment (sequince.target.TargetComponentFn)

• evaluation_key (Callable[[sequince.steps.context.StepContext], collections.abc.Hashable | None] | None)

evaluation_components(context)

Components needed for a full density evaluation, when known.

These are the components used to compute log_prob, such as during MCMC. They need not include every component the target supports: log_increment is included only when the density itself requires it. Other components can still be requested explicitly through prepare_evaluation(components=...).

When components=None, preparation uses this declaration to complete a partial cache and retain only these components. Returning None preserves the default full-evaluation contract for custom targets.

log_prob(particles, context, *, evaluation=None)

Return the current target log density.

log_increment(particles, context, *, evaluation=None)

Return the log-weight increment to the next target.

class sequince.density.TemperedDensity(log_initial, log_density_ratio, *, evaluation_key=None)

Bases: _DensityComponents, sequince.target.TemperedTarget

Tempered target defined by an initial density and a log-density ratio.

log_initial and log_density_ratio accept particles and optionally context. The target density is log_initial + beta * log_density_ratio. Weighting evaluates only the increment, reusing it from a compatible MCMC evaluation when available. MCMC evaluates and caches both components.

evaluation_key has the same meaning as for SequentialDensity; beta alone does not invalidate these endpoint components.

Parameters:

• log_initial (sequince.target.TargetComponentFn)

• log_density_ratio (sequince.target.TargetComponentFn)

• evaluation_key (Callable[[sequince.steps.context.StepContext], collections.abc.Hashable | None] | None)

log_initial(particles, context, *, evaluation=None)

Return the initial endpoint log density.

log_terminal(particles, context, *, evaluation=None)

Return the terminal endpoint log density.

log_increment(particles, context, *, evaluation=None)

Return the terminal-to-initial log-density ratio.

log_prob(particles, context, *, evaluation=None)

Return the current target log density.