valtype for AbstractHamiltonian and ProjectorMonteCarloProblem

error message if using complex Hamiltonian with ProjectorMonteCarloProblem

src/Hamiltonians/correlation_functions.jl

@@ -187,6 +187,7 @@ function Base.show(io::IO, g2::G2RealSpace{0,0})
 end
 
 LOStructure(::Type{<:G2RealSpace}) = IsDiagonal()
+Base.valtype(::G2RealSpace) = Float64 # needed because eltype is a vector
 
 num_offdiagonals(g2::G2RealSpace, _) = 0
 

src/Interfaces/hamiltonians.jl

@@ -59,7 +59,8 @@ See also [`Hamiltonians`](@ref Main.Hamiltonians), [`Interfaces`](@ref).
 """
 abstract type AbstractHamiltonian{T} end
 
-Base.eltype(::AbstractHamiltonian{T}) where {T} = T
+Base.eltype(::AbstractHamiltonian{T}) where {T} = T # could be vector value
+Base.valtype(h::AbstractHamiltonian) = eltype(h) # type of underlying scalar values
 
 """
     allows_address_type(operator, addr_or_type)

src/projector_monte_carlo_problem.jl

@@ -219,6 +219,12 @@ function ProjectorMonteCarloProblem(
         post_step_strategy = (post_step_strategy,)
     end
 
+    if !(eltype(hamiltonian)<: Real)
+        throw(ArgumentError("Only real-valued Hamiltonians are currently supported "*
+            "for ProjectorMonteCarloProblem. Please get in touch with the Rimu.jl " *
+            "developers if you need a complex-valued Hamiltonian!"))
+    end
+
     return ProjectorMonteCarloProblem{n_replicas,num_spectral_states(spectral_strategy)}(
         algorithm,
         hamiltonian,
@@ -240,3 +246,4 @@ end
 
 num_replicas(::ProjectorMonteCarloProblem{N}) where N = N
 num_spectral_states(::ProjectorMonteCarloProblem{<:Any,S}) where {S} = S
+Base.valtype(p::ProjectorMonteCarloProblem) = valtype(p.hamiltonian)

test/Hamiltonians.jl

@@ -912,6 +912,10 @@ using Rimu.Hamiltonians: circshift_dot
                 @test eval(Meta.parse(repr(g2_2))) == g2_2
                 @test eval(Meta.parse(repr(g2_3))) == g2_3
 
+                @test valtype(g2_1) == Float64
+                @test valtype(g2_2) == Float64
+                @test valtype(g2_3) == Float64
+
                 @test_throws ArgumentError G2RealSpace(CubicGrid(3), 1, 0)
                 @test_throws ArgumentError G2RealSpace(CubicGrid(2, 2), 0, 0)
                 @test_throws ArgumentError G2RealSpace(CubicGrid(1, 2, 3), -1, 2)

test/projector_monte_carlo_problem.jl

@@ -10,6 +10,7 @@ using OrderedCollections: freeze
     h = HubbardReal1D(BoseFS(1,3))
     p = ProjectorMonteCarloProblem(h; threading=true)
     @test p.hamiltonian == h
+    @test valtype(p.hamiltonian) == valtype(h)
 
     @test Rimu.num_replicas(p) == 1
     @test startswith(sprint(show, p), "ProjectorMonteCarloProblem with 1 replica(s)")
@@ -72,6 +73,11 @@ using OrderedCollections: freeze
     @test state_vectors(sm)[1] === dv1
     @test state_vectors(sm)[2] === dv2
     @test_throws BoundsError sm.state.spectral_states[3]
+
+    # complex Hamiltonian
+    h = HubbardReal1D(BoseFS(1, 3); u=1.0 + 1.0im)
+    @test valtype(h) <: Complex
+    @test_throws ArgumentError ProjectorMonteCarloProblem(h)
 end
 
 @testset "PMCSimulation" begin