Overload sparse for StateVectors (#36)

Author: david-pl

src/states.jl

@@ -195,6 +195,9 @@ function sparsebasisstate(::Type{T}, b::Basis, index::Integer) where T
 end
 sparsebasisstate(b::Basis, indices) = sparsebasisstate(ComplexF64, b, indices)
 
+SparseArrays.sparse(x::Ket) = Ket(x.basis,sparse(x.data))
+SparseArrays.sparse(x::Bra) = Bra(x.basis,sparse(x.data))
+
 # Helper functions to check validity of arguments
 function check_multiplicable(a::Bra, b::Ket)
     if a.basis != b.basis

test/test_states.jl

@@ -1,6 +1,7 @@
 using Test
 using QuantumOpticsBase
 using LinearAlgebra, Random
+using SparseArrays
 
 @testset "states" begin
 
@@ -119,6 +120,10 @@ x2 = basisstate(b2, 1)
 @test x1.data[2] == 1
 @test basisstate(b, [2, 1]) == x1 ⊗ x2
 
+# Conversion to sparse
+@test length(sparse(x1).data.nzval)==1
+@test sparse(x1').data isa SparseVector
+
 # Test permutating systems
 b1 = GenericBasis(2)
 b2 = GenericBasis(5)