Properly support scalars

Author: avik-pal

Project.toml

@@ -1,7 +1,7 @@
 name = "Sundials"
 uuid = "c3572dad-4567-51f8-b174-8c6c989267f4"
 authors = ["Chris Rackauckas <[email protected]>"]
-version = "4.23.0"
+version = "4.23.1"
 
 [deps]
 CEnum = "fa961155-64e5-5f13-b03f-caf6b980ea82"

src/common_interface/algorithms.jl

@@ -3,7 +3,7 @@
 # Abstract Types
 abstract type SundialsODEAlgorithm{Method, LinearSolver} <: DiffEqBase.AbstractODEAlgorithm end
 abstract type SundialsDAEAlgorithm{LinearSolver} <: DiffEqBase.AbstractDAEAlgorithm end
-abstract type SundialsNonlinearSolveAlgorithm{LinearSolver} end
+abstract type SundialsNonlinearSolveAlgorithm{LinearSolver} <: SciMLBase.AbstractNonlinearAlgorithm end
 
 SciMLBase.alg_order(alg::Union{SundialsODEAlgorithm, SundialsDAEAlgorithm}) = alg.max_order
 

src/common_interface/solve.jl

@@ -80,7 +80,11 @@ function DiffEqBase.__solve(prob::Union{
 
     f!(resid, u)
     retcode = interpret_sundials_retcode(flag)
-    DiffEqBase.build_solution(prob, alg, u, resid; retcode = retcode)
+    if prob.u0 isa Number
+        DiffEqBase.build_solution(prob, alg, u[1], resid[1]; retcode = retcode)
+    else
+        DiffEqBase.build_solution(prob, alg, u, resid; retcode = retcode)
+    end
 end
 
 function DiffEqBase.__init(prob::DiffEqBase.AbstractODEProblem{uType, tupType, isinplace},

test/kinsol_nonlinear_solve.jl

@@ -37,3 +37,20 @@ prob_oop = NonlinearProblem{false}(f_oop, u0)
     f_oop(sol.u, nothing)
     @test maximum(abs, du) < 1e-6
 end
+
+# Scalar
+f_scalar(u, p) = 2 - 2u
+u0 = 0.0
+prob_scalar = NonlinearProblem{false}(f_scalar, u0)
+
+@testset "linear_solver = $(linear_solver) | globalization_strategy = $(globalization_strategy)" for linear_solver in (:Dense,
+        :LapackDense, :GMRES, :FGMRES, :PCG, :TFQMR), globalization_strategy in (:LineSearch, :None)
+    local sol
+    alg = KINSOL(; linear_solver, globalization_strategy)
+    sol = solve(prob_scalar, alg; abstol)
+    @test SciMLBase.successful_retcode(sol.retcode)
+    @test sol.u isa Number
+
+    resid = f_scalar(sol.u, nothing)
+    @test abs(resid) < 1e-6
+end