# Docs DifferentialEquations.jl SecondOrderODEProblem

**URL:** <https://discourse.julialang.org/t/docs-differentialequations-jl-secondorderodeproblem/73773>\
**Category:** Numerics\
**Created:** [December 29, 2021, 5:57pm UTC](https://discourse.julialang.org/t/docs-differentialequations-jl-secondorderodeproblem/73773 "2021-12-29T17:57:02Z")\
**Posts on this page:** 2\
**Page:** 1

<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:** [December 29, 2021, 5:57pm UTC](https://discourse.julialang.org/t/docs-differentialequations-jl-secondorderodeproblem/73773/1 "2021-12-29T17:57:02Z")

</div>

What does the symbol f (as opposed to f1 or f2) in

SecondOrderODEProblem{isinplace}(f,du0,u0,tspan,p=NullParameters();kwargs…)

on the page [Dynamical, Hamiltonian, and 2nd Order ODE Solvers · DifferentialEquations.jl](https://diffeq.sciml.ai/stable/solvers/dynamical_solve/) refer to? That is, how is the second order ODE defined?

I saw the example at [2nd Order ODEs in Julia using DifferentialEquations - Stack Overflow](https://stackoverflow.com/questions/60180865/2nd-order-odes-in-julia-using-differentialequations)

Possibly, however, it might be valuable to make the documentation more explicit.

Thanks.

---

<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:** [December 30, 2021, 11:14am UTC](https://discourse.julialang.org/t/docs-differentialequations-jl-secondorderodeproblem/73773/2 "2021-12-30T11:14:10Z")

</div>

The answer to my question is given at [Dynamical, Hamiltonian and 2nd Order ODE Problems · DifferentialEquations.jl](https://diffeq.sciml.ai/stable/types/dynamical_types/) , i.e., the problems page (instead of the solvers page).

Thx for looking along. Domenico.