Add API to update iterative solver tolerances

ext/LinearSolveIterativeSolversExt.jl

@@ -105,7 +105,7 @@ function SciMLBase.solve!(cache::LinearCache, alg::IterativeSolversJL; kwargs...
         cache.Pr = Pr
         cache.precsisfresh = false
     end
-    if cache.isfresh || !(alg isa IterativeSolvers.GMRESIterable)
+    if cache.isfresh || !(cache.cacheval isa IterativeSolvers.GMRESIterable)
         solver = LinearSolve.init_cacheval(alg, cache.A, cache.b, cache.u, cache.Pl,
             cache.Pr,
             cache.maxiters, cache.abstol, cache.reltol,
@@ -149,4 +149,29 @@ function purge_history!(iter::IterativeSolvers.GMRESIterable, x, b)
     nothing
 end
 
+# The constructors above all set the tolerance as follows.
+#   tol = max(reltol * ||residual||, abstol)
+#
+# The iterable in turn is stored in `cache.cacheval`.
+function update_tolerances_iterativesolversjl!(iter, atol, rtol)
+    Rnorm = norm(iter.r)
+    iter.tol = max(rtol * Rnorm, atol)
+end
+function update_tolerances_iterativesolversjl!(iter::IterativeSolvers.GMRESIterable, atol, rtol)
+    Rnorm = iter.residual.current
+    iter.tol = max(rtol * Rnorm, atol)
+end
+function update_tolerances_iterativesolversjl!(iter::IterativeSolvers.MINRESIterable, atol, rtol)
+    Rnorm = norm(iter.v_curr)
+    iter.tol = max(rtol * Rnorm, atol)
+end
+function update_tolerances_iterativesolversjl!(iter::IterativeSolvers.IDRSIterable, atol, rtol)
+    Rnorm = iter.normR
+    iter.tol = max(rtol * Rnorm, atol)
+end
+
+function LinearSolve.update_tolerances_internal!(cache, alg::IterativeSolversJL, atol, rtol)
+    update_tolerances_iterativesolversjl!(cache.cacheval, atol, rtol)
+end
+
 end

ext/LinearSolveKrylovKitExt.jl

@@ -48,4 +48,6 @@ function SciMLBase.solve!(cache::LinearCache, alg::KrylovKitJL; kwargs...)
         iters = iters)
 end
 
+LinearSolve.update_tolerances_internal!(cache, alg::KrylovKitJL, atol, rtol) = nothing
+
 end

src/common.jl

@@ -478,3 +478,22 @@ function SciMLBase.solve(prob::StaticLinearProblem,
     return SciMLBase.build_linear_solution(
         alg, u, nothing, prob; retcode = ReturnCode.Success)
 end
+
+function update_tolerances!(cache; abstol = nothing, reltol = nothing)
+    if abstol !== nothing
+        cache.abstol = abstol
+    end
+    if reltol !== nothing
+        cache.reltol = reltol
+    end
+    update_tolerances_internal!(cache, cache.alg, abstol, reltol)
+end
+
+
+function update_tolerances_internal!(cache, alg::AbstractFactorization, abstol, reltol)
+    error("Cannot update tolerances for factorization.")
+end
+
+function update_tolerances_internal!(cache, alg::AbstractKrylovSubspaceMethod, abstol, reltol)
+    @warn "Tolerance update for Krylov subspace method '$typeof(alg)' not implemented." maxlog = 1
+end

src/iterative_wrappers.jl

@@ -338,3 +338,5 @@ function SciMLBase.solve!(cache::LinearCache, alg::KrylovJL; kwargs...)
     return SciMLBase.build_linear_solution(alg, cache.u, Ref(resid), cache;
         iters = stats.niter, retcode, stats)
 end
+
+update_tolerances_internal!(cache, alg::KrylovJL, atol, rtol) = nothing

test/basictests.jl

@@ -33,10 +33,17 @@ A4 = A2 .|> ComplexF32
 b4 = b2 .|> ComplexF32
 x4 = x2 .|> ComplexF32
 
+A5_ = A - 0.01Tridiagonal(ones(n,n)) + sparse([1], [8], 0.5, n,n)
+A5 = sparse(transpose(A5_) * A5_)
+x5 = zeros(n)
+u5 = ones(n)
+b5 = A5*u5
+
 prob1 = LinearProblem(A1, b1; u0 = x1)
 prob2 = LinearProblem(A2, b2; u0 = x2)
 prob3 = LinearProblem(A3, b3; u0 = x3)
 prob4 = LinearProblem(A4, b4; u0 = x4)
+prob5 = LinearProblem(A5, b5)
 
 cache_kwargs = (;abstol = 1e-8, reltol = 1e-8, maxiter = 30)
 
@@ -69,6 +76,19 @@ function test_interface(alg, prob1, prob2)
     return
 end
 
+function test_tolerance_update(alg, prob, u)
+    cache = init(prob, alg)
+    LinearSolve.update_tolerances!(cache; reltol = 1e-2, abstol=1e-8)
+    u1 = copy(solve!(cache).u)
+
+    LinearSolve.update_tolerances!(cache; reltol = 1e-8, abstol=1e-8)
+    u2 = solve!(cache).u
+
+    @test norm(u2 - u) < norm(u1 - u)
+
+    return
+end
+
 @testset "LinearSolve" begin
     @testset "Default Linear Solver" begin
         test_interface(nothing, prob1, prob2)
@@ -379,6 +399,7 @@ end
             @testset "$name" begin
                 test_interface(algorithm, prob1, prob2)
                 test_interface(algorithm, prob3, prob4)
+                test_tolerance_update(algorithm, prob5, u5)
             end
         end
     end
@@ -418,6 +439,7 @@ end
                 @testset "$(alg[1])" begin
                     test_interface(alg[2], prob1, prob2)
                     test_interface(alg[2], prob3, prob4)
+                    test_tolerance_update(alg[2], prob5, u5)
                 end
             end
         end
@@ -432,6 +454,7 @@ end
                 @testset "$(alg[1])" begin
                     test_interface(alg[2], prob1, prob2)
                     test_interface(alg[2], prob3, prob4)
+                    test_tolerance_update(alg[2], prob5, u5)
                 end
                 @test alg[2] isa KrylovKitJL
             end