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(WIP) Add ExtendingTraceTranslator. #370

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(WIP) Add ExtendingTraceTranslator. #370

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69 changes: 65 additions & 4 deletions src/inference/trace_translators.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -764,20 +764,20 @@ end
argdiffs::Tuple = (),
new_obs::ChoiceMap = EmptyChoiceMap(),
q_fwd::GenerativeFunction,
q_fwd_args::Tuple = ())
q_fwd_args::Tuple = ())

Constructor for a simple extending trace translator.

Run the translator with:

(output_trace, log_weight) = translator(input_trace)
"""
@with_kw struct SimpleExtendingTraceTranslator
@with_kw struct SimpleExtendingTraceTranslator
p_new_args::Tuple = ()
argdiffs::Tuple = ()
new_obs::ChoiceMap = EmptyChoiceMap()
q_fwd::GenerativeFunction
q_fwd_args::Tuple = ()
q_fwd_args::Tuple = ()
end

function (translator::SimpleExtendingTraceTranslator)(prev_model_trace::Trace)
Expand All @@ -801,6 +801,67 @@ function (translator::SimpleExtendingTraceTranslator)(prev_model_trace::Trace)
return (new_model_trace, log_weight)
end

##################################
# ExtendingTraceTranslator #
##################################

"""
translator = ExtendingTraceTranslator(;
p_new_args::Tuple = (),
argdiffs::Tuple = (),
new_obs::ChoiceMap = EmptyChoiceMap(),
q_fwd::GenerativeFunction,
q_fwd_args::Tuple = (),
f::Union{TraceTransformDSLProgram,Nothing} = nothing)

Constructor for a extending trace translator.

Run the translator with:

(output_trace, log_weight) = translator(input_trace)
"""
@with_kw struct ExtendingTraceTranslator
p_new_args::Tuple = ()
argdiffs::Tuple = ()
new_obs::ChoiceMap = EmptyChoiceMap()
q_fwd::GenerativeFunction
q_fwd_args::Tuple = ()
f::Union{TraceTransformDSLProgram,Nothing} = nothing # a bijection
end

function (translator::ExtendingTraceTranslator)(prev_model_trace::Trace)

# simulate from auxiliary program
forward_proposal_trace = simulate(translator.q_fwd, (prev_model_trace, translator.q_fwd_args...,))
forward_proposal_score = get_score(forward_proposal_trace)

# transform forward proposal
if translator.f === nothing
constraints = get_choices(forward_proposal_trace)
else
first_pass_results =
run_first_pass(translator.f, forward_proposal_trace, nothing)
log_abs_determinant =
jacobian_correction(translator.f, forward_proposal_trace,
nothing, first_pass_results, nothing)
constraints = first_pass_results.constraints
end

# computing the new trace via update
constraints = merge(constraints, translator.new_obs)
(new_model_trace, log_model_weight, _, discard) = update(
prev_model_trace, translator.p_new_args,
translator.argdiffs, constraints)

if !isempty(discard)
@error("can only extend the trace with random choices, cannot remove random choices")
error("Invalid ExtendingTraceTranslator")
end

log_weight = log_model_weight - forward_proposal_score + log_abs_determinant
return (new_model_trace, log_weight)
end

############################
# SymmetricTraceTranslator #
############################
Expand Down Expand Up @@ -884,7 +945,7 @@ function (translator::SymmetricTraceTranslator{<:Function})(
forward_retval = get_retval(forward_trace)
(new_model_trace, backward_choices, log_weight) = translator.involution(
prev_model_trace, forward_choices, forward_retval, translator.q_args)
(backward_score, backward_retval) = assess(translator.q, (new_model_trace, translator.q_args...), backward_choices)
(backward_score, backward_retval) = assess(translator.q, (new_model_trace, translator.q_args...), backward_choices)

log_weight += (backward_score - forward_score)

Expand Down