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Refactor names once again, add BigInt support
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@aryavorskiy
aryavorskiy committed Apr 15, 2024
1 parent fd3f1cd commit 7a28e0e
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Showing 2 changed files with 38 additions and 55 deletions.
75 changes: 33 additions & 42 deletions src/manybody.jl
View file
Original file line number Diff line number Diff line change
Expand Up @@ -24,9 +24,9 @@ function state_index(sv::SortedVector{T}, occ::T) where {T}
ret == length(sv) + 1 && return nothing
return sv.sortedvector[ret] == occ ? ret : nothing
end
state_index(occupations::AbstractVector{T}, state::T) where {T} = findfirst(==(state), occupations)
state_index(occupations::AbstractVector{T}, state::Base.RefValue{T}) where {T} = state_index(occupations, state[])
state_index(occupations::AbstractVector{T}, state::Any) where {T} = state_index(occupations, convert(T, state))
state_index(occupations::AbstractVector{T}, occ::T) where {T} = findfirst(==(occ), occupations)
state_index(occupations::AbstractVector{T}, occ::Base.RefValue{T}) where {T} = state_index(occupations, occ[])
state_index(occupations::AbstractVector{T}, occ::Any) where {T} = state_index(occupations, convert(T, occ))

"""
ManyBodyBasis(b, occupations)
Expand Down Expand Up @@ -145,16 +145,16 @@ number(mb::ManyBodyBasis) = number(ComplexF64, mb)
Operator ``|\\mathrm{to}⟩⟨\\mathrm{from}|`` transferring particles between modes.
Note that `to` and `from` can be collections of indices. The resulting operator in this case
will be equal to ``a^\\dagger_{to_1} a^\\dagger_{to_2} \\ldots a_{from_2} a_{from_1}``.
will be equal to ``\\ldots a^\\dagger_{to_2} a^\\dagger_{to_1} \\ldots a_{from_2} a_{from_1}``.
"""
function transition(::Type{T}, mb::ManyBodyBasis, to, from) where {T}
Is = Int[]
Js = Int[]
Vs = T[]
buffer = allocate_buffer(mb)
# <{m}_j| at_to a_from |{m}_i>
for (i, occ_i) in enumerate(mb.occupations)
C = state_transition!(buffer, occ_i, to, from)
for (i, occ) in enumerate(mb.occupations)
C = state_transition!(buffer, occ, to, from)
C === nothing && continue
j = state_index(mb.occupations, buffer)
j === nothing && continue
Expand Down Expand Up @@ -402,52 +402,43 @@ Base.@propagate_inbounds function state_transition!(buffer, occ::OccupationNumbe
end

"""
FermionBitstring(bits, n)
FermionBitstring{T}
Fermionic occupation state represented as a bitstring. The bitstring `bits` is represented
as an unsigned integer with the `n` least significant bits representing the occupation
state. The bitstring is assumed to be in the canonical form where the bits are ordered
from left to right with the most significant bit being the first mode.
Bitstring representation of a fermionic occupation state.
---
FermionBitstring(bits, n)
Create a `FermionBitstring` from an unsigned integer `bits` with the `n` least significant
bits representing the occupation state. All remaining bits are set to zero.
"""
struct FermionBitstring{T<:Unsigned}
struct FermionBitstring{T}
bits::T
n::Int
function FermionBitstring{T}(bits, n) where T<:Unsigned
n > sizeof(T) * 8 && throw(ArgumentError("n must be less than $(sizeof(T) * 8)"))
new{T}(bits, n)
end
function FermionBitstring(bits::T, n::Int) where T<:Unsigned
n > sizeof(T) * 8 && throw(ArgumentError("n must be less than $(sizeof(T) * 8)"))
nrest = sizeof(bits) * 8 - n
FermionBitstring{T}(UInt((bits << nrest) >>> nrest), n)
function FermionBitstring{T}(bits, n::Integer) where {T}
T<:Unsigned && n > sizeof(T) * 8 &&
throw(ArgumentError("n must be less than $(sizeof(T) * 8)"))
mask = T(1) << n - 1
new{T}(bits & mask, Int(n))
end
end
FermionBitstring(bits::Integer, n::Int) = FermionBitstring(unsigned(bits), n)
function FermionBitstring(bits::T, n::Integer) where T
FermionBitstring{T}(bits, n)
end

Base.zero(fb::FermionBitstring) = FermionBitstring(zero(fb.bits), fb.n)
Base.length(fb::FermionBitstring) = fb.n
Base.similar(::Type{FermionBitstring{T}}, n::Int) where {T} = FermionBitstring(zero(T), n)
function Base.similar(::Type{FermionBitstring}, n::Int)
for type in (UInt8, UInt16, UInt32, UInt64, UInt128)
n ≤ sizeof(type) * 8 && return FermionBitstring(zero(type), n)
end
throw(ArgumentError("n must be less than 128; got $n"))
end
function Base.convert(::Type{FermionBitstring{T}}, v::AbstractVector) where {T}
n = length(v)
n > sizeof(T) * 8 && throw(ArgumentError("n must be less than $(sizeof(T) * 8)"))
bits = zero(T)
for i in 1:n
v[i] in (0, 1) || throw(ArgumentError("Occupations must be 0 or 1"))
v[i] == 1 && (bits |= one(T) << (n - i))
function Base.convert(::Type{T}, v::AbstractVector) where {T<:FermionBitstring}
new_v = similar(T, length(v))
for i in 1:length(new_v)
new_v = Base.setindex(new_v, Bool(v[i]), i)
end
FermionBitstring{T}(bits, n)
return new_v
end
Base.copy(fb::FermionBitstring) = fb
allocate_buffer(fb::FermionBitstring) = Ref(fb)
Expand All @@ -462,27 +453,23 @@ Base.@propagate_inbounds function Base.getindex(fb::FermionBitstring, i::Int)
@boundscheck i in 1:fb.n || throw(BoundsError(fb, i))
Bool((fb.bits >>> (fb.n - i)) & 1)
end
Base.@propagate_inbounds function write_bit(fb::FermionBitstring, i::Int, value::Bool)
Base.@propagate_inbounds function Base.setindex(fb::FermionBitstring, value::Bool, i::Int)
@boundscheck i in 1:fb.n || throw(BoundsError(fb, i))
offset = fb.n - i
value ? FermionBitstring(fb.bits | (one(fb.bits) << offset), fb.n) :
FermionBitstring(fb.bits & ~(one(fb.bits) << offset), fb.n)
end
Base.@propagate_inbounds function write_bit(v::AbstractVector, i::Int, value::Bool)
setindex!(v, value, i)
return v
end
Base.@propagate_inbounds function state_transition!(buffer, occ::FermionBitstring, at_indices, a_indices)
factor = 1
for i in a_indices
occ[i] || return nothing
occ = write_bit(occ, i, false)
occ = setocc(occ, i, false)
ncomm = count_ones(occ.bits >>> (occ.n - i + 1))
isodd(ncomm) && (factor *= -1)
end
for i in at_indices
occ[i] && return nothing
occ = write_bit(occ, i, true)
occ = setocc(occ, i, true)
ncomm = count_ones(occ.bits >>> (occ.n - i + 1))
isodd(ncomm) && (factor *= -1)
end
Expand All @@ -502,7 +489,11 @@ function _distribute_bosons(Nparticles, Nmodes, index, occupations, results)
end
return results
end

Base.@propagate_inbounds setocc(fb::FermionBitstring, i::Int, value::Bool) = Base.setindex(fb, value, i)
Base.@propagate_inbounds function setocc(v::AbstractVector, i::Int, value::Bool)
setindex!(v, value, i)
return v
end
function _distribute_fermions(Nparticles, Nmodes, index, occupations, results)
if (Nmodes - index) + 1 < Nparticles
return results
Expand All @@ -512,9 +503,9 @@ function _distribute_fermions(Nparticles, Nmodes, index, occupations, results)
return results
end
for new_index in index:Nmodes - Nparticles + 1
occupations = write_bit(occupations, new_index, true)
occupations = setocc(occupations, new_index, true)
_distribute_fermions(Nparticles - 1, Nmodes, new_index + 1, occupations, results)
occupations = write_bit(occupations, new_index, false)
occupations = setocc(occupations, new_index, false)
end
return results
end
18 changes: 5 additions & 13 deletions test/test_manybody.jl
View file
Original file line number Diff line number Diff line change
Expand Up @@ -34,19 +34,11 @@ b = GenericBasis(Nmodes)
@test ManyBodyBasis(b, bosonstates(b, 1)) == ManyBodyBasis(b, fermionstates(b, 1))
@test ManyBodyBasis(b, bosonstates(b, 2)) != ManyBodyBasis(b, fermionstates(b, 2))

function _vec2fb(occ::AbstractVector{Int})
n = length(occ)
n > sizeof(UInt) * 8 && throw(ArgumentError("n must be less than $(sizeof(UInt) * 8)"))
bits = UInt(0)
for i in 1:n
if occ[i] != 0 && occ[i] != 1
throw(ArgumentError("Occupations must be 0 or 1"))
end
occ[i] == 1 && (bits |= UInt(1) << (n - i))
end
FermionBitstring(bits, n)
end
@test collect(fermionstates(FermionBitstring, b, 3)) == _vec2fb.(fermionstates(b, 3))
@test collect(fermionstates(FermionBitstring, b, 3)) ==
convert.(FermionBitstring, fermionstates(b, 3))
b2 = GenericBasis(130)
@test collect(fermionstates(FermionBitstring{BigInt}, b2, 2)) ==
convert.(FermionBitstring{BigInt}, fermionstates(b2, 2))

# Test basisstate
b_mb = ManyBodyBasis(b, bosonstates(b, 2))
Expand Down

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