Add solve function that allocates the initial guess/output vector.

This patch adds a function
solve(::HYPRESolver, ::HYPREMatrix, ::HYPREVector) which initializes an
output vector initialized to 0 and pass it to solve!.

src/solvers.jl

@@ -7,6 +7,30 @@ Abstract super type of all the wrapped HYPRE solvers.
 """
 abstract type HYPRESolver end
 
+# Generic fallback allocating a zero vector as initial guess
+# TODO: This should allocate x using the owned cols instead of rows of A/b, but currently
+#       it is assumed these are always equivalent.
+"""
+    solve(solver::HYPRESolver, A::HYPREMatrix, b::HYPREVector)
+
+Solve the linear system `A x = b` using `solver` and return the solution vector.
+
+This method allocates the initial guess/output vector `x`, initialized to 0.
+
+See also [`solve!`](@ref).
+"""
+solve(solver::HYPRESolver, A::HYPREMatrix, b::HYPREVector) = solve!(solver, zero(b), A, b)
+
+"""
+    solve!(solver::HYPRESolver, x::HYPREVector, A::HYPREMatrix, b::HYPREVector)
+
+Solve the linear system `A x = b` using `solver` with `x` as the initial guess.
+
+See also [`solve`](@ref).
+"""
+solve!(pcg::HYPRESolver, x::HYPREVector, A::HYPREMatrix, ::HYPREVector)
+
+
 #############
 # BoomerAMG #
 #############

test/runtests.jl

@@ -11,6 +11,7 @@ using SparseMatricesCSR
 using Test
 
 MPI.Init()
+HYPRE_Init()
 
 @testset "HYPREMatrix" begin
     H = HYPREMatrix()
@@ -264,6 +265,10 @@ end
     copy!(x, x_h)
     # Test result with direct solver
     @test x ≈ A \ b atol=tol
+    # Test without passing initial guess
+    x_h = HYPRE.solve(amg, A_h, b_h)
+    copy!(x, x_h)
+    @test x ≈ A \ b atol=tol
 end
 
 @testset "(ParCSR)PCG" begin
@@ -282,6 +287,10 @@ end
     copy!(x, x_h)
     # Test result with direct solver
     @test x ≈ A \ b atol=tol
+    # Test without passing initial guess
+    x_h = HYPRE.solve(pcg, A_h, b_h)
+    copy!(x, x_h)
+    @test x ≈ A \ b atol=tol
     # Solve with AMG preconditioner
     precond = HYPRE.BoomerAMG(; MaxIter = 1, Tol = 0.0)
     pcg = HYPRE.PCG(; Tol = tol, Precond = precond)
@@ -290,4 +299,8 @@ end
     copy!(x, x_h)
     # Test result with direct solver
     @test x ≈ A \ b atol=tol
+    # Test without passing initial guess
+    x_h = HYPRE.solve(pcg, A_h, b_h)
+    copy!(x, x_h)
+    @test x ≈ A \ b atol=tol
 end