Add test

Author: leburgel

test/bose_hubbard.jl

@@ -0,0 +1,40 @@
+using Test
+using TensorKit
+using MPSKit
+using MPSKitModels
+
+## Setup
+
+symmetry = U1Irrep
+cutoff = 3
+t = 1.0
+U = 10.0
+mu = 0.0
+n = 1
+lattice = InfiniteChain()
+
+Vspace = U1Space(0 => 8, 1 => 6, -1 => 6, 2 => 4, -2 => 4, 3 => 2, -3 => 2)
+
+alg = VUMPS(; maxiter=25, verbosity=0)
+
+# compare against higher-order analytic expansion from https://arxiv.org/pdf/1507.06426
+function exact_bose_hubbard_energy(; t=1.0, U=1.0)
+    J = t / U
+
+    E = 4 * U *
+        (-J^2 + J^4 + 68 / 9 * J^6 - 1267 / 81 * J^8 + 44171 / 1458 * J^10 -
+         4902596 / 6561 * J^12 -
+         8020902135607 / 2645395200 * J^14 - 32507578587517774813 / 466647713280000 * J^16)
+
+    return E
+end
+
+## Test
+
+@testset "Bose-Hubbard ground state" begin
+    H = bose_hubbard_model(symmetry, lattice; cutoff, t, U, mu, n)
+    ψ = InfiniteMPS([physicalspace(H, 1)], [Vspace])
+    @test imag(expectation_value(ψ, H)) ≈ 0 atol = 1e-10
+    ψ, envs, δ = find_groundstate(ψ, H, alg)
+    @test expectation_value(ψ, H, envs) ≈ exact_bose_hubbard_energy(; t, U) atol = 1e-2
+end

test/runtests.jl

@@ -37,6 +37,10 @@ end
     include("heisenberg.jl")
 end
 
+@testset "bose-hubbard model" begin
+    include("bose_hubbard.jl")
+end
+
 @testset "quantum potts model" begin
     include("quantum_potts.jl")
 end