LinearAlgebra: specialize is{hermitian,symmetric} for {Sym,}Tridiagonal #41037
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SyxP
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Jun 1, 2021
dkarrasch
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Jun 1, 2021
stdlib/LinearAlgebra/src/tridiag.jl
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| ishermitian(S::SymTridiagonal{<:Real}) = true | ||
| ishermitian(S::SymTridiagonal{<:Complex}) = all(x -> imag(x) == 0, S.dv) && all(x -> imag(x) == 0, S.ev) |
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| ishermitian(S::SymTridiagonal{<:Real}) = true | |
| ishermitian(S::SymTridiagonal{<:Complex}) = all(x -> imag(x) == 0, S.dv) && all(x -> imag(x) == 0, S.ev) | |
| ishermitian(S::SymTridiagonal) = isreal(S.dv) && isreal(S.ev) |
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Clearer, but slightly slower (by ~50ns) on my machine with S = SymTridiagonal(rand(100) .+ 0im, rand(100) .+ 0im).
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That's what isreal is good for, and we use it even internally in LinearAlgebra for that purpose.
dkarrasch
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Jun 2, 2021
sostock
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Jun 4, 2021
anaveragehuman
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…nal) SymTridiagonal allows `dv` and `ev` to have the same length, in which case the last element of `ev` isn't part of the matrix. Thus it doesn't matter, and should be ignored when checking if `ev` is real. Thanks to @sostock for pointing this out in JuliaLang#41037 (comment)
shirodkara
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johanmon
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