Fast basis (#287)

# New features

* `build_basis` and `build_sparse_matrix_from_LO` are now parallel.
* `build_basis` and `build_sparse_matrix_from_LO` now support an
argument `max_depth` which limits the number of steps of the breadth
first search to perform.
* New method `build_basis(::AbstractFockAddress)` which is much faster.

# Bugfixes

* `OccupationNumberFS` now has the same ordering as `BoseFS`.
* Fix a bug where `MatrixHamiltonian` would not work with sparse
matrices that have implicit zeros on the diagonal.

src/BitStringAddresses/occupationnumberfs.jl

@@ -66,7 +66,14 @@ end
 Base.reverse(ofs::OccupationNumberFS) = OccupationNumberFS(reverse(ofs.onr))
 
 onr(ofs::OccupationNumberFS) = ofs.onr
-Base.isless(a::OccupationNumberFS, b::OccupationNumberFS) = isless(b.onr, a.onr)
+function Base.isless(a::OccupationNumberFS{M}, b::OccupationNumberFS{M}) where {M}
+    # equivalent to `isless(reverse(a.onr), reverse(b.onr))`
+    i = length(a.onr)
+    while i > 1 && a.onr[i] == b.onr[i]
+        i -= 1
+    end
+    return isless(a.onr[i], b.onr[i])
+end
 # reversing the order here to make it consistent with BoseFS
 Base.:(==)(a::OccupationNumberFS, b::OccupationNumberFS) = a.onr == b.onr
 Base.hash(ofs::OccupationNumberFS, h::UInt) = hash(ofs.onr, h)

src/ExactDiagonalization/ExactDiagonalization.jl

@@ -25,14 +25,16 @@ using CommonSolve: CommonSolve, solve, init
 using VectorInterface: VectorInterface, add
 using OrderedCollections: freeze
 using NamedTupleTools: delete
+using StaticArrays: setindex
 
 using Rimu: Rimu, DictVectors, Hamiltonians, Interfaces, BitStringAddresses, replace_keys,
     clean_and_warn_if_others_present
 using ..Interfaces: AbstractDVec, AbstractHamiltonian, AdjointUnknown,
     diagonal_element, offdiagonals, starting_address, LOStructure, IsHermitian
-using ..BitStringAddresses: AbstractFockAddress
+using ..BitStringAddresses: AbstractFockAddress, BoseFS, FermiFS, CompositeFS, near_uniform
 using ..DictVectors: FrozenDVec, PDVec, DVec
-using ..Hamiltonians: check_address_type, dimension, ParitySymmetry, TimeReversalSymmetry
+using ..Hamiltonians: allows_address_type, check_address_type, dimension,
+    ParitySymmetry, TimeReversalSymmetry
 
 
 export ExactDiagonalizationProblem, KrylovKitSolver, LinearAlgebraSolver
@@ -42,6 +44,8 @@ export BasisSetRepresentation, build_basis
 export sparse # from SparseArrays
 
 
+include("basis_breadth_first_search.jl")
+include("basis_fock.jl")
 include("basis_set_representation.jl")
 include("algorithms.jl")
 include("exact_diagonalization_problem.jl")