# \`sol.du\` is \`nothing\` in \`DAESolution\`

**URL:** <https://discourse.julialang.org/t/sol-du-is-nothing-in-daesolution/33636>\
**Category:** Numerics\
**Tags:** diffeq\
**Created:** [January 21, 2020, 8:32pm UTC](https://discourse.julialang.org/t/sol-du-is-nothing-in-daesolution/33636 "2020-01-21T20:32:37Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![zekeriya.sari](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/zekeriya.sari/32/13695_2.png) [@zekeriya.sari](https://discourse.julialang.org/u/zekeriya.sari)\
**Post date:** [January 21, 2020, 8:32pm UTC](https://discourse.julialang.org/t/sol-du-is-nothing-in-daesolution/33636/1 "2020-01-21T20:32:37Z")

</div>

I tried the `DAEProblem` example in the manual of the `DifferentialEquations`. The example is given is here.

```julia
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?