# Find out which solver was used in automatic solver selection

**URL:** <https://discourse.julialang.org/t/find-out-which-solver-was-used-in-automatic-solver-selection/131564>\
**Category:** General Usage\
**Tags:** differentialequation\
**Created:** [August 12, 2025, 1:57pm UTC](https://discourse.julialang.org/t/find-out-which-solver-was-used-in-automatic-solver-selection/131564 "2025-08-12T13:57:37Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![diffeqslvr](https://avatars.discourse-cdn.com/v4/letter/d/f475e1/32.png) [@diffeqslvr](https://discourse.julialang.org/u/diffeqslvr)\
**Post date:** [August 12, 2025, 1:57pm UTC](https://discourse.julialang.org/t/find-out-which-solver-was-used-in-automatic-solver-selection/131564/1 "2025-08-12T13:57:37Z")

</div>

In julia, I am using an automatic solver selection to solve differential equations using the DifferentialEquations package. I would like to know which solver was used in the end, but when I run `sol.alg`, I get

```julia-auto
CompositeAlgorithm(; algs = (Tsit5{typeof(OrdinaryDiffEqCore.trivial_limiter!), typeof(OrdinaryDiffEqCore.trivial_limiter!), Static.False}(OrdinaryDiffEqCore.trivial_limiter!, OrdinaryDiffEqCore.trivial_limiter!, static(false)), Vern7{typeof(OrdinaryDiffEqCore.trivial_limiter!), typeof(OrdinaryDiffEqCore.trivial_limiter!), Static.False}(OrdinaryDiffEqCore.trivial_limiter!, OrdinaryDiffEqCore.trivial_limiter!, static(false), true), Rosenbrock23{1, false, Nothing, typeof(OrdinaryDiffEqCore.DEFAULT_PRECS), Val{:forward}, true, nothing, typeof(OrdinaryDiffEqCore.trivial_limiter!), typeof(OrdinaryDiffEqCore.trivial_limiter!)}(nothing, OrdinaryDiffEqCore.DEFAULT_PRECS, OrdinaryDiffEqCore.trivial_limiter!, OrdinaryDiffEqCore.trivial_limiter!), Rodas5P{1, false, Nothing, typeof(OrdinaryDiffEqCore.DEFAULT_PRECS), Val{:forward}, true, nothing, typeof(OrdinaryDiffEqCore.trivial_limiter!), typeof(OrdinaryDiffEqCore.trivial_limiter!)}(nothing, OrdinaryDiffEqCore.DEFAULT_PRECS, OrdinaryDiffEqCore.trivial_limiter!, OrdinaryDiffEqCore.trivial_limiter!), FBDF{5, 1, false, Nothing, NLNewton{Rational{Int64}, Rational{Int64}, Rational{Int64}, Rational{Int64}}, typeof(OrdinaryDiffEqCore.DEFAULT_PRECS), Val{:forward}, true, nothing, Nothing, Nothing, typeof(OrdinaryDiffEqCore.trivial_limiter!)}(Val{5}(), nothing, NLNewton{Rational{Int64}, Rational{Int64}, Rational{Int64}, Rational{Int64}}(1//100, 10, 1//5, 1//5, false, true, 0//1), OrdinaryDiffEqCore.DEFAULT_PRECS, nothing, nothing, :linear, :Standard, OrdinaryDiffEqCore.trivial_limiter!), FBDF{5, 1, false, KrylovJL{typeof(Krylov.gmres!), Int64, Nothing, Tuple{}, Base.Pairs{Symbol, Union{}, Tuple{}, @NamedTuple{}}}, NLNewton{Rational{Int64}, Rational{Int64}, Rational{Int64}, Rational{Int64}}, typeof(OrdinaryDiffEqCore.DEFAULT_PRECS), Val{:forward}, true, nothing, Nothing, Nothing, typeof(OrdinaryDiffEqCore.trivial_limiter!)}(Val{5}(), KrylovJL{typeof(Krylov.gmres!), Int64, Nothing, Tuple{}, Base.Pairs{Symbol, Union{}, Tuple{}, @NamedTuple{}}}(Krylov.gmres!, 0, 0, nothing, (), Base.Pairs{Symbol, Union{}, Tuple{}, @NamedTuple{}}()), NLNewton{Rational{Int64}, Rational{Int64}, Rational{Int64}, Rational{Int64}}(1//100, 10, 1//5, 1//5, false, true, 0//1), OrdinaryDiffEqCore.DEFAULT_PRECS, nothing, nothing, :linear, :Standard, OrdinaryDiffEqCore.trivial_limiter!)), choice_function = OrdinaryDiffEqCore.AutoSwitchCache{Tuple{Tsit5{typeof(OrdinaryDiffEqCore.trivial_limiter!), typeof(OrdinaryDiffEqCore.trivial_limiter!), Static.False}, Vern7{typeof(OrdinaryDiffEqCore.trivial_limiter!), typeof(OrdinaryDiffEqCore.trivial_limiter!), Static.False}}, Tuple{Rosenbrock23{0, false, Nothing, typeof(OrdinaryDiffEqCore.DEFAULT_PRECS), Val{:forward}, true, nothing, typeof(OrdinaryDiffEqCore.trivial_limiter!), typeof(OrdinaryDiffEqCore.trivial_limiter!)}, Rodas5P{0, false, Nothing, typeof(OrdinaryDiffEqCore.DEFAULT_PRECS), Val{:forward}, true, nothing, typeof(OrdinaryDiffEqCore.trivial_limiter!), typeof(OrdinaryDiffEqCore.trivial_limiter!)}, FBDF{5, 0, false, Nothing, NLNewton{Rational{Int64}, Rational{Int64}, Rational{Int64}, Rational{Int64}}, typeof(OrdinaryDiffEqCore.DEFAULT_PRECS), Val{:forward}, true, nothing, Nothing, Nothing, typeof(OrdinaryDiffEqCore.trivial_limiter!)}, FBDF{5, 0, false, KrylovJL{typeof(Krylov.gmres!), Int64, Nothing, Tuple{}, Base.Pairs{Symbol, Union{}, Tuple{}, @NamedTuple{}}}, NLNewton{Rational{Int64}, Rational{Int64}, Rational{Int64}, Rational{Int64}}, typeof(OrdinaryDiffEqCore.DEFAULT_PRECS), Val{:forward}, true, nothing, Nothing, Nothing, typeof(OrdinaryDiffEqCore.trivial_limiter!)}}, Rational{Int64}, Int64}(5, 0, (Tsit5{typeof(OrdinaryDiffEqCore.trivial_limiter!), typeof(OrdinaryDiffEqCore.trivial_limiter!), Static.False}(OrdinaryDiffEqCore.trivial_limiter!, OrdinaryDiffEqCore.trivial_limiter!, static(false)), Vern7{typeof(OrdinaryDiffEqCore.trivial_limiter!), typeof(OrdinaryDiffEqCore.trivial_limiter!), Static.False}(OrdinaryDiffEqCore.trivial_limiter!, OrdinaryDiffEqCore.trivial_limiter!, static(false), true)), (Rosenbrock23{0, false, Nothing, typeof(OrdinaryDiffEqCore.DEFAULT_PRECS), Val{:forward}, true, nothing, typeof(OrdinaryDiffEqCore.trivial_limiter!), typeof(OrdinaryDiffEqCore.trivial_limiter!)}(nothing, OrdinaryDiffEqCore.DEFAULT_PRECS, OrdinaryDiffEqCore.trivial_limiter!, OrdinaryDiffEqCore.trivial_limiter!), Rodas5P{0, false, Nothing, typeof(OrdinaryDiffEqCore.DEFAULT_PRECS), Val{:forward}, true, nothing, typeof(OrdinaryDiffEqCore.trivial_limiter!), typeof(OrdinaryDiffEqCore.trivial_limiter!)}(nothing, OrdinaryDiffEqCore.DEFAULT_PRECS, OrdinaryDiffEqCore.trivial_limiter!, OrdinaryDiffEqCore.trivial_limiter!), FBDF{5, 0, false, Nothing, NLNewton{Rational{Int64}, Rational{Int64}, Rational{Int64}, Rational{Int64}}, typeof(OrdinaryDiffEqCore.DEFAULT_PRECS), Val{:forward}, true, nothing, Nothing, Nothing, typeof(OrdinaryDiffEqCore.trivial_limiter!)}(Val{5}(), nothing, NLNewton{Rational{Int64}, Rational{Int64}, Rational{Int64}, Rational{Int64}}(1//100, 10, 1//5, 1//5, false, true, 0//1), OrdinaryDiffEqCore.DEFAULT_PRECS, nothing, nothing, :linear, :Standard, OrdinaryDiffEqCore.trivial_limiter!), FBDF{5, 0, false, KrylovJL{typeof(Krylov.gmres!), Int64, Nothing, Tuple{}, Base.Pairs{Symbol, Union{}, Tuple{}, @NamedTuple{}}}, NLNewton{Rational{Int64}, Rational{Int64}, Rational{Int64}, Rational{Int64}}, typeof(OrdinaryDiffEqCore.DEFAULT_PRECS), Val{:forward}, true, nothing, Nothing, Nothing, typeof(OrdinaryDiffEqCore.trivial_limiter!)}(Val{5}(), KrylovJL{typeof(Krylov.gmres!), Int64, Nothing, Tuple{}, Base.Pairs{Symbol, Union{}, Tuple{}, @NamedTuple{}}}(Krylov.gmres!, 0, 0, nothing, (), Base.Pairs{Symbol, Union{}, Tuple{}, @NamedTuple{}}()), NLNewton{Rational{Int64}, Rational{Int64}, Rational{Int64}, Rational{Int64}}(1//100, 10, 1//5, 1//5, false, true, 0//1), OrdinaryDiffEqCore.DEFAULT_PRECS, nothing, nothing, :linear, :Standard, OrdinaryDiffEqCore.trivial_limiter!)), true, 10, 3, 9//10, 9//10, 2, false, 5, 5),)

```

is there any way of knowing which solver was picked by julia?

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<div class="post-metadata">

**Author:** ![ziolai](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ziolai/32/23422_2.png) [@ziolai](https://discourse.julialang.org/u/ziolai)\
**Post date:** [August 12, 2025, 2:47pm UTC](https://discourse.julialang.org/t/find-out-which-solver-was-used-in-automatic-solver-selection/131564/2 "2025-08-12T14:47:15Z")

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Not sure.`sol.stats` ?

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<div class="post-metadata">

**Author:** ![diffeqslvr](https://avatars.discourse-cdn.com/v4/letter/d/f475e1/32.png) [@diffeqslvr](https://discourse.julialang.org/u/diffeqslvr)\
**Post date:** [August 13, 2025, 7:38am UTC](https://discourse.julialang.org/t/find-out-which-solver-was-used-in-automatic-solver-selection/131564/4 "2025-08-13T07:38:04Z")

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I only get statistics about the number of function evaluations and Jacobian creations:

```julia-auto
SciMLBase.DEStats
Number of function 1 evaluations: 13773
Number of function 2 evaluations: 0
Number of W matrix evaluations: 1455
Number of linear solves: 9516
Number of Jacobians created: 13
Number of nonlinear solver iterations: 9396
Number of nonlinear solver convergence failures: 0
Number of fixed-point solver iterations: 0
Number of fixed-point solver convergence failures: 0
Number of rootfind condition calls: 1945
Number of accepted steps: 1945
Number of rejected steps: 205

```

---

<div class="post-metadata">

**Author:** ![ChrisRackauckas](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chrisrackauckas/32/77_2.png) [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)\
**Post date:** [August 13, 2025, 3:20pm UTC](https://discourse.julialang.org/t/find-out-which-solver-was-used-in-automatic-solver-selection/131564/5 "2025-08-13T15:20:20Z")

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`sol.alg_choice`, where the integer is the `sol.alg.algs[i]`

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<div class="post-metadata">

**Author:** ![diffeqslvr](https://avatars.discourse-cdn.com/v4/letter/d/f475e1/32.png) [@diffeqslvr](https://discourse.julialang.org/u/diffeqslvr)\
**Post date:** [August 14, 2025, 10:13am UTC](https://discourse.julialang.org/t/find-out-which-solver-was-used-in-automatic-solver-selection/131564/6 "2025-08-14T10:13:55Z")

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To be very clear, is the following correct?

`sol.alg_choice` gives a vector of integers whose length is the number of saved time steps in sol.t. Each integer corresponds to the index of the algorithm in `sol.alg.algs` that was used for the corresponding time step.

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<div class="post-metadata">

**Author:** ![ChrisRackauckas](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chrisrackauckas/32/77_2.png) [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)\
**Post date:** [August 14, 2025, 10:16am UTC](https://discourse.julialang.org/t/find-out-which-solver-was-used-in-automatic-solver-selection/131564/7 "2025-08-14T10:16:20Z")

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Yes