Truncation composition

ext/MatrixAlgebraKitChainRulesCoreExt.jl

@@ -176,4 +176,4 @@ function ChainRulesCore.rrule(::typeof(right_polar!), A::AbstractMatrix, PWᴴ,
     return PWᴴ, right_polar_pullback
 end
 
-end
+end

src/algorithms.jl

@@ -178,4 +178,4 @@ macro check_size(x, sz, size=:size)
                           string($sz)
                    szx == $sz || throw(DimensionMismatch($err))
                end)
-end
+end

src/implementations/orthnull.jl

@@ -215,4 +215,4 @@ function right_null!(A::AbstractMatrix, Nᴴ; kwargs...)
     else
         throw(ArgumentError("`right_null!` received unknown value `kind = $kind`"))
     end
-end
+end

src/implementations/truncation.jl

@@ -11,10 +11,17 @@
     if isnothing(maxrank) && isnothing(atol) && isnothing(rtol)
         return NoTruncation()
     elseif isnothing(maxrank)
-        @assert isnothing(rtol) "TODO: rtol"
-        return trunctol(atol)
+        atol = @something atol 0
+        rtol = @something rtol 0
+        return TruncationKeepAbove(atol, rtol)
     else
-        return truncrank(maxrank)
+        if isnothing(atol) && isnothing(rtol)
+            return truncrank(maxrank)
+        else
+            atol = @something atol 0
+            rtol = @something rtol 0
+            return truncrank(maxrank) & TruncationKeepAbove(atol, rtol)
+        end
     end
 end
 
@@ -82,6 +89,20 @@
 """
 truncabove(atol) = TruncationKeepFiltered(≤(atol) ∘ abs)
 
+"""
+    TruncationComposition(trunc1::TruncationStrategy, trunc2::TruncationStrategy)
+
+Compose two truncation strategies, keeping values common between the two strategies.
+"""
+struct TruncationComposition{T1<:TruncationStrategy,T2<:TruncationStrategy} <:
+       TruncationStrategy
+    trunc1::T1
+    trunc2::T2
+end
+function Base.:&(trunc1::TruncationStrategy, trunc2::TruncationStrategy)
+    return TruncationComposition(trunc1, trunc2)
+end
+
 # truncate!
 # ---------
 # Generic implementation: `findtruncated` followed by indexing
@@ -147,6 +168,12 @@
     return 1:i
 end
 
+function findtruncated(values::AbstractVector, strategy::TruncationComposition)
+    ind1 = findtruncated(values, strategy.trunc1)
+    ind2 = findtruncated(values, strategy.trunc2)
+    return ind1 ∩ ind2
+end
+
 """
     TruncatedAlgorithm(alg::AbstractAlgorithm, trunc::TruncationAlgorithm)
 

src/interface/orthnull.jl

@@ -224,4 +224,4 @@ function right_null!(A::AbstractMatrix; kwargs...)
 end
 function right_null(A::AbstractMatrix; kwargs...)
     return right_null!(copy_input(right_null, A); kwargs...)
-end
+end

src/pullbacks/polar.jl

@@ -58,4 +58,4 @@ function right_polar_pullback!(ΔA::AbstractMatrix, PWᴴ, ΔPWᴴ)
         ΔA .+= PΔWᴴ
     end
     return ΔA
-end
+end

test/chainrules.jl

@@ -356,4 +356,4 @@ end
         test_rrule(config, right_null, A; fkwargs=(; kind=:lqpos), output_tangent=ΔNᴴ,
                    atol=atol, rtol=rtol, rrule_f=rrule_via_ad, check_inferred=false)
     end
-end
+end

test/orthnull.jl

@@ -209,4 +209,4 @@ end
             end
         end
     end
-end
+end

test/svd.jl

@@ -108,3 +108,29 @@ end
         end
     end
 end
+
+@testset "svd_trunc! mix maxrank and tol for T = $T" for T in (Float32, Float64, ComplexF32,
+                                                               ComplexF64)
+    rng = StableRNG(123)
+    if LinearAlgebra.LAPACK.version() < v"3.12.0"
+        algs = (LAPACK_DivideAndConquer(), LAPACK_QRIteration(), LAPACK_Bisection())
+    else
+        algs = (LAPACK_DivideAndConquer(), LAPACK_QRIteration(), LAPACK_Bisection(),
+                LAPACK_Jacobi())
+    end
+    m = 4
+    @testset "algorithm $alg" for alg in algs
+        U = qr_compact(randn(rng, T, m, m))[1]
+        S = Diagonal([0.9, 0.3, 0.1, 0.01])
+        Vᴴ = qr_compact(randn(rng, T, m, m))[1]
+        A = U * S * Vᴴ
+
+        U1, S1, V1ᴴ = svd_trunc(A; alg, trunc=(; rtol=0.2, maxrank=1))
+        @test length(S1.diag) == 1
+        @test S1.diag ≈ S.diag[1:1] rtol = sqrt(eps(real(T)))
+
+        U2, S2, V2ᴴ = svd_trunc(A; alg, trunc=(; rtol=0.2, maxrank=3))
+        @test length(S2.diag) == 2
+        @test S2.diag ≈ S.diag[1:2] rtol = sqrt(eps(real(T)))
+    end
+end