Ignore dt checking when initial guess is provided

Author: ErikQQY

lib/BoundaryValueDiffEqCore/src/utils.jl

@@ -207,7 +207,6 @@ end
 function __extract_problem_details(
         prob, u0::SciMLBase.ODESolution; dt = 0.0, check_positive_dt::Bool = false)
     # Problem passes in a initial guess function
-    check_positive_dt && dt ≤ 0 && throw(ArgumentError("dt must be positive"))
     _u0 = first(u0.u)
     _t = u0.t
     return Val(true), eltype(_u0), length(_u0), (length(_t) - 1), _u0

test/misc/initial_guess_tests.jl

@@ -0,0 +1,39 @@
+@testitem "Initial guess providing" begin
+    using BoundaryValueDiffEq
+    tspan = (0.0, pi / 2)
+    function simplependulum!(du, u, p, t)
+        θ = u[1]
+        dθ = u[2]
+        du[1] = dθ
+        du[2] = -9.81 * sin(θ)
+    end
+    function bc!(residual, u, p, t)
+        residual[1] = u(pi / 4)[1] + pi / 2
+        residual[2] = u(pi / 2)[1] - pi / 2
+    end
+    u0 = [pi / 2, pi / 2]
+    prob = BVProblem(simplependulum!, bc!, u0, tspan)
+    sol1 = solve(prob, MIRK4(), dt = 0.05)
+
+    # Solution
+    prob1 = BVProblem(simplependulum!, bc!, sol1, tspan)
+    sol2 = solve(prob1, MIRK4())
+    @test SciMLBase.successful_retcode(sol2)
+
+    sol3 = solve(prob1, RadauIIa5())
+    @test SciMLBase.successful_retcode(sol3)
+
+    sol4 = solve(prob1, LobattoIIIa4(nested_nlsolve = true))
+    @test SciMLBase.successful_retcode(sol4)
+
+    # VectorOfArray
+    prob2 = BVProblem(simplependulum!, bc!, VectorOfArray(sol1.u), tspan)
+    sol2 = solve(prob2, MIRK4())
+    @test SciMLBase.successful_retcode(sol2)
+
+    sol3 = solve(prob2, RadauIIa5())
+    @test SciMLBase.successful_retcode(sol3)
+
+    sol4 = solve(prob2, LobattoIIIa4(nested_nlsolve = true))
+    @test SciMLBase.successful_retcode(sol4)
+end