Add mapping from InfinitePEPO to InfinitePEPS or InfinitePartitionFunction

Author: lkdvos

src/networks/tensors.jl

@@ -123,3 +123,23 @@ function physicalspace(t::PEPOTensor)
     return codomain_physicalspace(t)
 end
 virtualspace(t::PEPOTensor, dir) = space(t, dir + 2)
+
+"""
+    $(SIGNATURES)
+
+Fuse the physical indices of a PEPO tensor, obtaining a PEPS tensor.
+"""
+function fuse_physicalspaces(O::PEPOTensor)
+    F = isomorphism(Int, fuse(codomain(O)), codomain(O))
+    return F * O, F
+end
+
+"""
+    $(SIGNATURES)
+
+Trace out the physical indices of a PEPO tensor, obtaining a partition function tensor.
+"""
+function contract_physicalspaces(O::PEPOTensor)
+    @plansor t[W S; N E] := O[p p; N E S W]
+    return t
+end

src/operators/infinitepepo.jl

@@ -173,6 +173,23 @@ function InfiniteSquareNetwork(top::InfinitePEPS, mid::InfinitePEPO, bot::Infini
     )
 end
 
+## Conversion to states
+
+function InfinitePartitionFunction(ρ::InfinitePEPO)
+    size(ρ, 3) == 1 || throw(DimensionMismatch("Only single-layer density matrices can be converted to partition functions"))
+    return InfinitePartitionFunction(
+        contract_physicalspaces.(reshape(unitcell(ρ), size(ρ, 1), size(ρ, 2)))
+    )
+end
+
+function InfinitePEPS(ρ::InfinitePEPO)
+    size(ρ, 3) == 1 || throw(DimensionMismatch("Only single-layer density matrices can be converted to partition functions"))
+    return InfinitePEPS(
+        first.(fuse_physicalspaces.(reshape(unitcell(ρ), size(ρ, 1), size(ρ, 2))))
+    )
+end
+
+
 ## Vector interface
 
 VI.scalartype(::Type{NT}) where {NT <: InfinitePEPO} = scalartype(eltype(NT))