Hi all,

I apologize if it’s a possibly stupid question, but I am trying to calculate the Hessian of a function that internally performs the integration of a differential equation. What I am currently doing is this:

```
using Zygote, DifferentialEquations
function der!(du, u, p, t)
du[1] = -p[1] * u[1]
end
function cost_for_hessian(params)
prob_uode_pred = ODEProblem{true}(der!, [10.0], (0, 10))
solutions = solve(prob_uode_pred, Tsit5(), p=params, saveat=[10.0], sensealg=ForwardDiffSensitivity())
return sum(abs2.((solutions)))
end
sensitivity_analysis_hessian = hessian(p -> cost_for_hessian(p), [2.0])
```

When I try to execute the code (julia version 1.9.1, Zygote v0.6.61, DifferentialEquations v7.7.0), I get the following error: ERROR: Cannot determine ordering of Dual tags.

Could anyone tell me if what I am trying to do is feasible and how to do it?

Thank you in advance!