First version of a tempered target

src/targets/TemperedTarget.jl

@@ -0,0 +1,50 @@
+"""
+$SIGNATURES
+
+Tempers the given target's log_potential by a factor `beta`. 
+Note that this action is performed on the entire density and so the resulting target need not be normalizable. 
+Caution should therefore be taken when this (possibly improper) target is used.
+
+$FIELDS
+"""
+@auto struct TemperedLogPotential{L}
+    """The encapsulated LogPotential."""
+    base_log_potential::L
+
+    """
+    Inverse temperature (factor by which the base log potential is scaled) with 0 < beta ≤ 1. 
+    E.g., beta = 1 corresponds to the exact same functionality as a LogPotential that was 
+    not wrapped inside a TemperedLogPotential. 
+    """
+    beta::Float64
+end
+
+base_log_potential(log_potential::TemperedLogPotential) = log_potential.base_log_potential
+
+# evaluate the log density
+(ref::TemperedLogPotential)(x) = ref.beta * base_log_potential(ref)(x) 
+
+# initialization
+initialization(target::TemperedLogPotential, rng::AbstractRNG, replica_index::Int) =
+    initialization(base_log_potential(target), rng, replica_index) 
+
+# default explorer 
+default_explorer(target::TemperedLogPotential) = default_explorer(base_log_potential(target)) 
+
+# default reference
+default_reference(target::TemperedLogPotential) = default_reference(base_log_potential(target)) 
+
+# iid sampling (doing this would be incorrect....)
+function sample_iid!(ref::TemperedLogPotential, replica::Replica{<:AbstractArray}, shared)
+    if ref.beta == 1.0
+        sample_iid!(base_log_potential(ref), replica, shared)
+    else 
+        sample_iid!(ref, replica, shared) # defaults to using MCMC, so not really IID
+        # this can be overwritten by the user if they know how to sample IID from the tempered target
+    end
+end
+
+# make it conform to the LogDensityProblems interface (if implemented)
+LogDensityProblems.logdensity(log_potential::TemperedLogPotential, x) = log_potential(x)
+LogDensityProblems.dimension(log_potential::TemperedLogPotential) = 
+    LogDensityProblems.dimension(base_log_potential(log_potential))