From 92d1ee4f362f0009f2f9167b1da4281b420f5b61 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jorge=20A=2E=20P=C3=A9rez-Hern=C3=A1ndez?=
 <perez.hz@gmail.com>
Date: Wed, 10 Apr 2024 09:37:39 +0200
Subject: [PATCH] wip

---
 ext/TaylorIntegrationDiffEq.jl | 27 ++++++++++++++++++++++++---
 test/common.jl                 | 13 +++++++++++++
 test/runtests.jl               | 18 +++++++++---------
 3 files changed, 46 insertions(+), 12 deletions(-)

diff --git a/ext/TaylorIntegrationDiffEq.jl b/ext/TaylorIntegrationDiffEq.jl
index f0afddeb..79c1c84a 100644
--- a/ext/TaylorIntegrationDiffEq.jl
+++ b/ext/TaylorIntegrationDiffEq.jl
@@ -9,19 +9,21 @@ if isdefined(Base, :get_extension)
     import OrdinaryDiffEq: OrdinaryDiffEqAdaptiveAlgorithm,
         OrdinaryDiffEqConstantCache, OrdinaryDiffEqMutableCache,
         alg_order, alg_cache, initialize!, perform_step!, @unpack,
-        @cache, stepsize_controller!, step_accept_controller!, _ode_addsteps!
+        @cache, stepsize_controller!, step_accept_controller!, _ode_addsteps!,
+        _ode_interpolant!, _ode_interpolant
 else
     using ..OrdinaryDiffEq
     import ..OrdinaryDiffEq: OrdinaryDiffEqAdaptiveAlgorithm,
         OrdinaryDiffEqConstantCache, OrdinaryDiffEqMutableCache,
         alg_order, alg_cache, initialize!, perform_step!, @unpack,
-        @cache, stepsize_controller!, step_accept_controller!, _ode_addsteps!
+        @cache, stepsize_controller!, step_accept_controller!, _ode_addsteps!,
+        _ode_interpolant!, _ode_interpolant
 end
 
 using StaticArrays: SVector, SizedArray
 using RecursiveArrayTools: ArrayPartition
 
-import DiffEqBase: ODEProblem, solve, ODE_DEFAULT_NORM
+import DiffEqBase: ODEProblem, solve, ODE_DEFAULT_NORM, interp_summary
 
 # TODO: check which keywords work fine
 const warnkeywords = (:save_idxs, :d_discontinuities, :unstable_check, :save_everystep,
@@ -286,6 +288,25 @@ function _ode_addsteps!(k, t, uprev, u, dt, f, p, cache::TaylorMethodCache,
     nothing
 end
 
+function interp_summary(::Type{cacheType}, dense::Bool) where {cacheType <: TaylorMethodCache}
+    dense ? "Taylor series polynomial evaluation" : "1st order linear"
+end
+
+# idxs gives back multiple values
+function _ode_interpolant!(out, Θ, dt, y₀, y₁, k, cache::TaylorMethodCache, idxs, T::Type{Val{TI}}) where {TI}
+    Θm1 = Θ - 1
+    @inbounds for i in eachindex(out)
+        out[i] = cache.uT[i](Θm1*dt)
+    end
+    out
+end
+
+# when idxs gives back a single value
+function _ode_interpolant(Θ, dt, y₀, y₁, k, cache::TaylorMethodCache, idxs, T::Type{Val{TI}}) where {TI}
+    Θm1 = Θ - 1
+    return cache.uT[idxs](Θm1*dt)
+end
+
 @inline TaylorIntegration.__jetcoeffs!(::Val{false}, f::ODEFunction, t, x::Taylor1{U}, params,
     rv::TaylorIntegration.RetAlloc{Taylor1{U}}) where {U} = TaylorIntegration.__jetcoeffs!(Val(false), f.f, t, x, params)
 @inline TaylorIntegration.__jetcoeffs!(::Val{true},  f::ODEFunction, t, x::Taylor1{U}, params,
diff --git a/test/common.jl b/test/common.jl
index 8d3ddcc9..173220b2 100644
--- a/test/common.jl
+++ b/test/common.jl
@@ -99,6 +99,19 @@ import Logging: Warn
             harmosc!, u0, tspan[1], tspan[2], order, abstol))
         @test sol.t == tv1
         @test xv1[end,:] == sol.u[end]
+        @test DiffEqBase.interp_summary(sol.interp) == "Taylor series polynomial evaluation"
+        tvsol = range(tspan[1], tspan[2], length=10)
+        tv2, xv2, psol2 = (@test_logs min_level=Logging.Warn taylorinteg(
+            harmosc!, u0, tspan[1], tspan[2], order, abstol, Val(true)))
+        Θ = rand()
+        dt_test = (tv2[end]-tv2[end-1])
+        t_test = tv2[end-1] + Θ*dt_test
+        @test norm(sol(t_test) .- psol2[end,:]( Θ*dt_test ), Inf) < 1e-14
+        Θ = rand()
+        Θm1 = Θ - 1
+        dt_test = (tv2[end-1]-tv2[end-2])
+        t_test = tv2[end-2] + Θ*dt_test
+        @test norm( sol(t_test) .- psol2[end,:]( Θm1*dt_test ) ) < 1e-14
     end
 
     @testset "Test discrete callback in common interface" begin
diff --git a/test/runtests.jl b/test/runtests.jl
index 0c2fc5e3..253274de 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1,16 +1,16 @@
 # This file is part of the TaylorIntegration.jl package; MIT licensed
 
 testfiles = (
-    "one_ode.jl",
-    "many_ode.jl",
-    "complex.jl",
-    "jettransport.jl",
-    "lyapunov.jl",
-    "bigfloats.jl",
+    # "one_ode.jl",
+    # "many_ode.jl",
+    # "complex.jl",
+    # "jettransport.jl",
+    # "lyapunov.jl",
+    # "bigfloats.jl",
     "common.jl",
-    "rootfinding.jl",
-    "taylorize.jl",
-    "aqua.jl",
+    # "rootfinding.jl",
+    # "taylorize.jl",
+    # "aqua.jl",
     )
 
 for file in testfiles