29 lines
991 B
Julia
29 lines
991 B
Julia
using LinearAlgebra
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"Sum over array while minimizing catastrophic cancellation as much as possible"
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function better_sum(arr::Array{Float64})
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pos_arr = arr[arr .> 0]
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neg_arr = arr[arr .< 0]
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sort!(pos_arr)
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sort!(neg_arr, rev=true)
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return sum(pos_arr) + sum(neg_arr)
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end
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better_sum(arr::Array{ComplexF64}) = better_sum(real.(arr)) + 1im * better_sum(imag.(arr))
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"The triangle inequality for angular momenta"
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triangle_ineq(l1, l2, L) = abs(l1 - l2) ≤ L && L ≤ (l1 + l2)
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"Index of the nearest value in a list to a given reference point"
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nearestIndex(list::Array, ref) = argmin(norm.(list .- ref))
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"Nearest value in a list to a given reference point"
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nearest(list::Array, ref) = list[nearestIndex(list, ref)]
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"Simple implementation of the Kronecker sum"
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function kron_sum(A::AbstractMatrix, B::AbstractMatrix)
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@assert size(A, 1) == size(A, 2) && size(B, 1) == size(B, 2) "Matrices should be square"
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return kron(A, I(size(B, 1))) + kron(B, I(size(A, 1)))
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end |