37 lines
1.1 KiB
Julia
37 lines
1.1 KiB
Julia
"""
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wlmetric_ball(S::AbstractVector{<:GroupElem}
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[, center=one(first(S)); radius=2, op=*])
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Compute metric ball as a list of elements of non-decreasing length, given the
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word-length metric on the group generated by `S`. The ball is centered at `center`
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(by default: the identity element). `radius` and `op` keywords specify the
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radius and multiplication operation to be used.
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"""
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function wlmetric_ball(
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S::AbstractVector{T},
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center::T = one(first(S));
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radius = 2,
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op = *,
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) where {T}
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ball = [center]
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sizes = [1]
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if radius ≤ 0
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return ball, sizes[2:end]
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else
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ball = union!(ball, [center * s for s in S])
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push!(sizes, length(ball))
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if radius == 1
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return ball, sizes[2:end]
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else
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for _ in 2:radius
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new = collect(
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op(o, s) for o in @view(ball[sizes[end-1]:end]) for s in S
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)
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ball = union!(ball, new)
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push!(sizes, length(ball))
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end
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end
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return ball, sizes[2:end]
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end
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# return wlmetric_ball_serial(S, center; radius = radius, op = op)
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end
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