Add BandedPlusSemiseparable and QR#53
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dlfivefifty wants to merge 23 commits intoJuliaLinearAlgebra:masterfrom
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Add BandedPlusSemiseparable and QR#53dlfivefifty wants to merge 23 commits intoJuliaLinearAlgebra:masterfrom
dlfivefifty wants to merge 23 commits intoJuliaLinearAlgebra:masterfrom
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## master #53 +/- ##
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+ Coverage 89.70% 95.41% +5.70%
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Lines 272 523 +251
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+ Hits 244 499 +255
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@TaoChenImperial I added a function level to separate out the pre-computation. Unfortunately there's still allocation: julia> U,V = randn(n,r), randn(n,r); W,S = randn(n,p), randn(n,p); A = BandedPlusSemiseparableQRPerturbedFactors(U,V,W,S,B); storage = zeros(T,A.n), UᵀU_lookup_table(A), ūw̄_sum_lookup_table(A), d_extra_lookup_table(A); @time bandedplussemi_qr!(A, storage...);
0.000354 seconds (12.13 k allocations: 725.844 KiB)I'll put some comments in the review so you can see where some of the issues are. |
dlfivefifty
commented
Nov 12, 2025
| """ | ||
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| struct BandedPlusSemiseparableQRPerturbedFactors{T} <: LayoutMatrix{T} | ||
| n::Int # matrix size |
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We don't need to store this as it can be inferred from size(B,n)
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| struct BandedPlusSemiseparableQRPerturbedFactors{T} <: LayoutMatrix{T} | ||
| n::Int # matrix size | ||
| r::Int # lower rank |
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This can be inferred from size(U,2)
| struct BandedPlusSemiseparableQRPerturbedFactors{T} <: LayoutMatrix{T} | ||
| n::Int # matrix size | ||
| r::Int # lower rank | ||
| p::Int # upper rank |
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This can be inferred from size(W,2)
| n::Int # matrix size | ||
| r::Int # lower rank | ||
| p::Int # upper rank | ||
| l::Int # lower bandwidth |
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l and m can be inferred from bandwidths(B)
| j = A.j[] | ||
| UᵀA_1 = (A.U[j+1:min(A.l+j+1,A.n),:])'*A.B[j+1:min(A.l+j+1,A.n),j+1] + UᵀU[j+2,:,:]*A.V[j+1,:] #the j+1th column of UᵀA | ||
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| k̄ = A.V[j+1,:] + A.Q * A.S[j+1,1:A.p] + A.K * UᵀA_1 |
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This is allocating. You should use views.
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And in all the code below.
| end | ||
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| function update_next_submatrix!(A, k̄, b, τ, w̄₁, ū₁, d₁, f, d̄, c₁, c₂, c₃, c₄, c₅, c₆) | ||
| Q_prev = A.Q[:,:] |
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These are all allocating. Why do we need them?
| ūw̄_sum = zeros(A.n, A.r, A.p) | ||
| ūw̄_sum_current = zeros(A.r, A.p) | ||
| for t in 1:A.n | ||
| ūw̄_sum[t,:,:] = ūw̄_sum_current[:,:] |
| ūw̄_sum_current = zeros(A.r, A.p) | ||
| for t in 1:A.n | ||
| ūw̄_sum[t,:,:] = ūw̄_sum_current[:,:] | ||
| ūw̄_sum_current[:,:] += A.U[t,:] * (A.W[t,1:A.p])' |
| function fast_UᵀA(U, V, W, S, B, j) | ||
| # compute U[j,end]ᵀ*A[j:end,j:end] where A = tril(UV',-1) + B + triu(WS',1) in O(n) | ||
| n = size(U,1) | ||
| r = size(U,2) |
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Suggested change
| r = size(U,2) | |
| (n,r) = size(U) |
dlfivefifty
commented
Nov 18, 2025
src/semiseparableqr.jl
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| end | ||
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| function bandedplussemi_qr!(A, τ, tables...) | ||
| n = A.n | ||
| n = size(A.B, 1) | ||
| for i in 1 : n-1 | ||
| onestep_qr!(A, τ, tables...) | ||
| end | ||
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| A.B[n,n] = A[n,n] |
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add a comment explaining what this is doing
src/semiseparableqr.jl
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| Eₛ_prev = copy(A.Eₛ) | ||
| Xₛ_prev = copy(A.Xₛ) | ||
| Yₛ_prev = copy(A.Yₛ) | ||
| Zₛ_prev = copy(A.Zₛ) |
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Why do we need to make copies?
src/semiseparableqr.jl
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| b[1:min(A.l-1,length(b))] += (A.Xₛ * A.S[j+1,1:A.p] + A.Yₛ * UᵀA_1 + A.Zₛ[:,1])[2:min(A.l,length(b)+1)] | ||
| b = A.B[j+2:min(l+j+1, n), j+1] | ||
| if l > 0 || m > 0 | ||
| b[1:min(l-1,length(b))] .+= view((A.Xₛ * view(A.S, j+1, 1:p) + A.Yₛ * UᵀA_1 + view(A.Zₛ, :, 1)), 2:min(l,length(b)+1)) |
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Can this be rewritten as muladd! calls?
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| b[1:min(l-1,length(b))] .+= view((A.Xₛ * view(A.S, j+1, 1:p) + A.Yₛ * UᵀA_1 + view(A.Zₛ, :, 1)), 2:min(l,length(b)+1)) | |
| kr = 2:min(l,length(b)+1) | |
| v = view(b, kr .- 1) | |
| T = eltype(A) | |
| mul!(v, view(A.Xₛ, kr,:), view(A.S, j+1, 1:p), one(T), one(T)) | |
| mul!(v, view(A.Yₛ,kr,:), UᵀA_1, one(T), one(T)) | |
| v .+= view(A.Zₛ, kr, 1) |
dlfivefifty
commented
Nov 20, 2025
src/semiseparableqr.jl
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| ūw̄_sum_current = zeros(eltype(A), r, p) | ||
| for t in 1:n | ||
| ūw̄_sum[t,:,:] .= ūw̄_sum_current | ||
| ūw̄_sum_current .+= view(A.U, t, :) * (view(A.W, t, 1:p))' |
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| ūw̄_sum_current .+= view(A.U, t, :) * (view(A.W, t, 1:p))' | |
| mul!(ūw̄_sum_current, view(A.U, t, :), view(A.W, t, 1:p)', one(eltype(A)), one(eltype(A))) |
src/semiseparableqr.jl
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| b[1:min(A.l-1,length(b))] += (A.Xₛ * A.S[j+1,1:A.p] + A.Yₛ * UᵀA_1 + A.Zₛ[:,1])[2:min(A.l,length(b)+1)] | ||
| b = A.B[j+2:min(l+j+1, n), j+1] | ||
| if l > 0 || m > 0 | ||
| b[1:min(l-1,length(b))] .+= view((A.Xₛ * view(A.S, j+1, 1:p) + A.Yₛ * UᵀA_1 + view(A.Zₛ, :, 1)), 2:min(l,length(b)+1)) |
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| b[1:min(l-1,length(b))] .+= view((A.Xₛ * view(A.S, j+1, 1:p) + A.Yₛ * UᵀA_1 + view(A.Zₛ, :, 1)), 2:min(l,length(b)+1)) | |
| kr = 2:min(l,length(b)+1) | |
| v = view(b, kr .- 1) | |
| T = eltype(A) | |
| mul!(v, view(A.Xₛ, kr,:), view(A.S, j+1, 1:p), one(T), one(T)) | |
| mul!(v, view(A.Yₛ,kr,:), UᵀA_1, one(T), one(T)) | |
| v .+= view(A.Zₛ, kr, 1) |
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