I tried the `DAEProblem`

example in the manual of the `DifferentialEquations`

. The example is given is here.

```
using DifferentialEquations
using Sundials
function f(out,du,u,p,t)
out[1] = - 0.04u[1] + 1e4*u[2]*u[3] - du[1]
out[2] = + 0.04u[1] - 3e7*u[2]^2 - 1e4*u[2]*u[3] - du[2]
out[3] = u[1] + u[2] + u[3] - 1.0
end
u₀ = [1.0, 0, 0]
du₀ = [-0.04, 0.04, 0.0]
tspan = (0.0,100000.0)
differential_vars = [true,true,false]
prob = DAEProblem(f,du₀,u₀,tspan,differential_vars=differential_vars)
sol = solve(prob,IDA())
```

From the solution `sol`

, I found that `sol.du`

is nothing. But, I think this should not be the case. Am I missing something?