Branch ambiguity fixed
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@ -20,7 +20,7 @@ c0 = find_zero(quick_extrapolate, 0.85)
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# Calculation of training and extrapolating E
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training_c = range(1.2, 0.9, 9) # original: range(1.35, 0.9, 5)
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training_E = [quick_pole_E(V_system(c)) for c in training_c]
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training_k = new_sqrt.(2μ .* training_E)
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training_k = alt_sqrt.(2μ .* training_E)
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extrapolating_c = range(0.78, 0.45, 7) # original: range(0.75, 0.40, 8)
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exact_E = [quick_pole_E(V_system(c)) for c in extrapolating_c]
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@ -28,7 +28,7 @@ exact_E = [quick_pole_E(V_system(c)) for c in extrapolating_c]
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order::Int = ceil((length(training_c) - 1) / 2) # order of the Pade approximant
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# Solve coefficients as a linear system
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M_left_element(c, i) = complex(c - c0)^(i/2)
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M_left_element(c, i) = alt_sqrt(c - c0)^i
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M_left = M_left_element.(training_c, (0:order)')
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M_right = -training_k .* M_left[:, 2:end] # remove the first column
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M = hcat(M_left, M_right) # M = [M_left | M_right]
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@ -37,14 +37,11 @@ a = sol[1:order+1]
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b = [1; sol[order+2:end]]
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# Pade approximant
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polynomial(a, c) = sum(i -> a[i+1] * complex(c - c0)^(i/2), 0:order)
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polynomial(a, c) = sum(i -> a[i+1] * alt_sqrt(c - c0)^i, 0:order)
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pade_approx(c) = polynomial(a, c) / polynomial(b, c)
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# Extrapolate
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extrapolated_k = pade_approx.([training_c; extrapolating_c])
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if real.(extrapolated_k[end]) < 0 # flip if following anti-resonance
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extrapolated_k = -conj.(extrapolated_k)
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end
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extrapolated_E = (extrapolated_k .^ 2) / (2μ)
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# Plotting
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@ -2,8 +2,8 @@ using LinearAlgebra, DelimitedFiles, SparseArrays
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@enum coordinate_system jacobi src
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"Square root function with the branch cut along the postive real axis"
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new_sqrt(x::Number)::ComplexF64 = im * sqrt(complex(-x))
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"Square root function with the branch cut along the postive imaginary axis"
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alt_sqrt(x::Number)::ComplexF64 = sqrt(im * x) / sqrt(im)
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"Sum over array while minimizing catastrophic cancellation as much as possible"
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function better_sum(arr::Array{T}) where T<:Real
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