implement in-place ldiv! for Cholesky factorization (#547)

* implement solve2 without workspace arguments

* implement in-place ldiv! for Cholesky factorization

* ldiv! with Dense not required

* import ldiv! for tests

* safer

* fix Dense case and add more tests

* rearrange wrap_dense_and_ptr

* more tests

src/solvers/cholmod.jl

@@ -18,7 +18,7 @@ using LinearAlgebra
 using LinearAlgebra: RealHermSymComplexHerm, AdjOrTrans
 import LinearAlgebra: (\), AdjointFactorization,
                  cholesky, cholesky!, det, diag, ishermitian, isposdef,
-                 issuccess, issymmetric, ldlt, ldlt!, logdet,
+                 issuccess, issymmetric, ldiv!, ldlt, ldlt!, logdet,
                  lowrankdowndate, lowrankdowndate!, lowrankupdate, lowrankupdate!
 
 using SparseArrays
@@ -913,6 +913,32 @@ function Base.convert(::Type{Dense{Tnew}}, A::Dense{T}) where {Tnew, T}
 end
 Base.convert(::Type{Dense{T}}, A::Dense{T}) where T = A
 
+# Just calling Dense(x) or Dense(b) will allocate new
+# `cholmod_dense_struct`s in CHOLMOD. Instead, we want to reuse
+# the existing memory. We can do this by creating new
+# `cholmod_dense_struct`s and filling them manually.
+function wrap_dense_and_ptr(x::StridedVecOrMat{T}) where {T <: VTypes}
+    dense_x = cholmod_dense_struct()
+    dense_x.nrow = size(x, 1)
+    dense_x.ncol = size(x, 2)
+    dense_x.nzmax = length(x)
+    dense_x.d = stride(x, 2)
+    dense_x.x = pointer(x)
+    dense_x.z = C_NULL
+    dense_x.xtype = xtyp(eltype(x))
+    dense_x.dtype = dtyp(eltype(x))
+    return dense_x, pointer_from_objref(dense_x)
+end
+# We need to use a special handling for the case of `Dense`
+# input arrays since the `pointer` refers to the pointer to the
+# `cholmod_dense`, not to the array values themselves as for
+# standard arrays.
+function wrap_dense_and_ptr(x::Dense{T}) where {T <: VTypes}
+    dense_x_ptr = x.ptr
+    dense_x = unsafe_load(dense_x_ptr)
+    return dense_x, pointer_from_objref(dense_x)
+end
+
 # This constructor assumes zero based colptr and rowval
 function Sparse(m::Integer, n::Integer,
         colptr0::Vector{Ti}, rowval0::Vector{Ti},
@@ -1913,6 +1939,66 @@ const AbstractSparseVecOrMatInclAdjAndTrans = Union{AbstractSparseVecOrMat, AdjO
     throw(ArgumentError("self-adjoint sparse system solve not implemented for sparse rhs B," *
         " consider to convert B to a dense array"))
 
+# in-place ldiv!
+for TI in IndexTypes
+    @eval function ldiv!(x::StridedVecOrMat{T},
+                         L::Factor{T, $TI},
+                         b::StridedVecOrMat{T}) where {T<:VTypes}
+        if x === b
+            throw(ArgumentError("output array must not be aliased with input array"))
+        end
+        if size(L, 1) != size(b, 1)
+            throw(DimensionMismatch("Factorization and RHS should have the same number of rows. " *
+                "Factorization has $(size(L, 2)) rows, but RHS has $(size(b, 1)) rows."))
+        end
+        if size(L, 2) != size(x, 1)
+            throw(DimensionMismatch("Factorization and solution should match sizes. " *
+                "Factorization has $(size(L, 1)) columns, but solution has $(size(x, 1)) rows."))
+        end
+        if size(x, 2) != size(b, 2)
+            throw(DimensionMismatch("Solution and RHS should have the same number of columns. " *
+                "Solution has $(size(x, 2)) columns, but RHS has $(size(b, 2)) columns."))
+        end
+        if !issuccess(L)
+            s = unsafe_load(pointer(L))
+            if s.is_ll == 1
+                throw(LinearAlgebra.PosDefException(s.minor))
+            else
+                throw(LinearAlgebra.ZeroPivotException(s.minor))
+            end
+        end
+
+        # Just calling Dense(x) or Dense(b) will allocate new
+        # `cholmod_dense_struct`s in CHOLMOD. Instead, we want to reuse
+        # the existing memory. We can do this by creating new
+        # `cholmod_dense_struct`s and filling them manually.
+        dense_x, dense_x_ptr = wrap_dense_and_ptr(x)
+        dense_b, dense_b_ptr = wrap_dense_and_ptr(b)
+
+        X_Handle = Ptr{cholmod_dense_struct}(dense_x_ptr)
+        Y_Handle = Ptr{cholmod_dense_struct}(C_NULL)
+        E_Handle = Ptr{cholmod_dense_struct}(C_NULL)
+        status = GC.@preserve x dense_x b dense_b begin
+            $(cholname(:solve2, TI))(
+                CHOLMOD_A, L,
+                Ref(dense_b), C_NULL,
+                Ref(X_Handle), C_NULL,
+                Ref(Y_Handle),
+                Ref(E_Handle),
+                getcommon($TI))
+        end
+        if Y_Handle != C_NULL
+            free!(Y_Handle)
+        end
+        if E_Handle != C_NULL
+            free!(E_Handle)
+        end
+        @assert !iszero(status)
+
+        return x
+    end
+end
+
 ## Other convenience methods
 function diag(F::Factor{Tv, Ti}) where {Tv, Ti}
     f = unsafe_load(typedpointer(F))

test/cholmod.jl

@@ -13,7 +13,7 @@ using Random
 using Serialization
 using LinearAlgebra:
     I, cholesky, cholesky!, det, diag, eigmax, ishermitian, isposdef, issuccess,
-    issymmetric, ldlt, ldlt!, logdet, norm, opnorm, Diagonal, Hermitian, Symmetric,
+    issymmetric, ldiv!, ldlt, ldlt!, logdet, norm, opnorm, Diagonal, Hermitian, Symmetric,
     PosDefException, ZeroPivotException, RowMaximum
 using SparseArrays
 using SparseArrays: getcolptr
@@ -138,6 +138,9 @@ Random.seed!(123)
     @test CHOLMOD.isvalid(chma)
     @test unsafe_load(pointer(chma)).is_ll == 1    # check that it is in fact an LLt
     @test chma\b ≈ x
+    x2 = zero(x)
+    @inferred ldiv!(x2, chma, b)
+    @test x2 ≈ x
     @test nnz(chma) == 489
     @test nnz(cholesky(A, perm=1:size(A,1))) > nnz(chma)
     @test size(chma) == size(A)
@@ -281,6 +284,37 @@ end
     end
 end
 
+@testset "ldiv! $Tv $Ti" begin
+    local A, x, x2, b, X, X2, B
+    A = sprand(10, 10, 0.1)
+    A = I + A * A'
+    A = convert(SparseMatrixCSC{Tv,Ti}, A)
+    factor = cholesky(A)
+
+    x = fill(Tv(1), 10)
+    b = A * x
+    x2 = zero(x)
+    @inferred ldiv!(x2, factor, b)
+    @test x2 ≈ x
+
+    X = fill(Tv(1), 10, 5)
+    B = A * X
+    X2 = zero(X)
+    @inferred ldiv!(X2, factor, B)
+    @test X2 ≈ X
+
+    c = fill(Tv(1), size(x, 1) + 1)
+    C = fill(Tv(1), size(X, 1) + 1, size(X, 2))
+    y = fill(Tv(1), size(x, 1) + 1)
+    Y = fill(Tv(1), size(X, 1) + 1, size(X, 2))
+    @test_throws DimensionMismatch ldiv!(y, factor, b)
+    @test_throws DimensionMismatch ldiv!(Y, factor, B)
+    @test_throws DimensionMismatch ldiv!(x2, factor, c)
+    @test_throws DimensionMismatch ldiv!(X2, factor, C)
+    @test_throws DimensionMismatch ldiv!(X2, factor, b)
+    @test_throws DimensionMismatch ldiv!(x2, factor, B)
+end
+
 end #end for Ti ∈ itypes
 
 for Tv ∈ (Float32, Float64)
@@ -365,9 +399,9 @@ end
     @test isa(CHOLMOD.eye(3), CHOLMOD.Dense{Float64})
 end
 
-@testset "Core functionality ($elty, $elty2)" for 
-    elty in (Tv, Complex{Tv}), 
-    Tv2 in (Float32, Float64), 
+@testset "Core functionality ($elty, $elty2)" for
+    elty in (Tv, Complex{Tv}),
+    Tv2 in (Float32, Float64),
     elty2 in (Tv2, Complex{Tv2}),
     Ti ∈ itypes
     A1 = sparse(Ti[1:5; 1], Ti[1:5; 2], elty <: Real ? randn(Tv, 6) : complex.(randn(Tv, 6), randn(Tv, 6)))
@@ -972,7 +1006,7 @@ end
     f = ones(size(K, 1))
     u = K \ f
     residual = norm(f - K * u) / norm(f)
-    @test residual < 1e-6 
+    @test residual < 1e-6
 end
 
 @testset "wrapped sparse matrices" begin