71 lines
2.4 KiB
Julia
71 lines
2.4 KiB
Julia
Float = Union{Float32,Float64}
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"A few-body system defined by its physical parameters"
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struct system{T}
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d::Int
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n::Int
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N::Int
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L::T
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μ::T
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function system{T}(d::Int, n::Int, N::Int, L::Real, μ::Real) where {T<:Float}
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return new{T}(d, n, N, convert(T, L), convert(T, μ))
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end
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end
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norm_square(x::Array{Int})::Int = sum(x .* x)
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"Eq (46): Partial derivative matrix element for 1 degree of freedom"
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function ∂_1DOF(s::system{T}, k::Int, l::Int)::Complex{T} where {T<:Float}
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if k == l
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return -im * (π / s.L)
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else
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return (π / s.L) * (-1)^(k - l) * exp(-im * π * (k - l) / s.N) / sin(π * (k - l) / s.N)
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end
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end
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"Which index (dimension of the multidimensional array) corresponds to spatial dimension 'dim' and particle 'p'?"
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which_index(s::system, dim::Int, p::Int)::Int = (dim - 1) * (s.n - 1) + p
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"Δk (distance in terms of lattice paramter) between two particles along the given dimension"
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function get_Δk(s::system, i::CartesianIndex, dim::Int, p1::Int, p2::Int)::Int
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if p1 == p2
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return 0
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elseif p1 == s.n
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return -(i[which_index(s, dim, p2)] - s.N ÷ 2 - 1)
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elseif p2 == s.n
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return i[which_index(s, dim, p1)] - s.N ÷ 2 - 1
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else
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return i[which_index(s, dim, p1)] - i[which_index(s, dim, p2)]
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end
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end
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"Calculate diagonal elements of the V matrix"
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function calculate_Vs(V_twobody::Function, s::system{T}, ϕ::T, n_image::Int)::Array{Complex{T}} where {T<:Float}
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coeff² = (exp(im * ϕ) * s.L / s.N)^2
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images = collect.(Iterators.product(fill(-n_image:n_image, s.d)...)) # TODO: Learn how to use tuples instead of vectors
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Vs = zeros(Complex{T}, fill(s.N, s.d * (s.n - 1))...)
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Threads.@threads for i in CartesianIndices(Vs)
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for p1 in 1:s.n
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for p2 in (p1 + 1):s.n
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min_Δk = Array{Int}(undef, s.d)
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for dim in 1:s.d
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Δk = get_Δk(s, i, dim, p1, p2)
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if Δk > s.N ÷ 2
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min_Δk[dim] = Δk - s.N
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elseif Δk < -s.N ÷ 2
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min_Δk[dim] = Δk + s.N
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else
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min_Δk[dim] = Δk
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end
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end
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for image in images
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Δk² = norm_square(min_Δk .- (s.N .* image))
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Vs[i] += V_twobody(Δk² * coeff²)
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end
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end
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end
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end
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return Vs
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end
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