Is there an elegant way of extracting the upper triangle of a matrix as a vector using Base? Besides, of course, writing something like function vec_triu(M::AbstractMatrix{T}) where T m, n = size(M) m == n || throw(error("not square")) l = n*(n+1) ÷ 2 v = Vector{T}(l) k = 0 …

Not that I know, but just FYI, you need to write out the loop; your function allocates (on 0.7 from this week). This does not even make your code longer or harder to read. @inbounds for ell=1:i v[k + ell] = M[ell, i] end

Vector of upper triangle

General Usage

GunnarFarneback December 14, 2017, 3:57pm 2

M[triu(trues(M))]

See also Half Vectorization

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Vector of upper triangle

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