This is the opposite way of writing things than in the OpenFOAM example! If we want to couple to OpenFOAM we have to change that.
#### Code related questions
What is the best way to reload a checkpoint?
Saving `sol` and then
1. reloading `sol` via `GridVariables->update(sol)` followed by a `GridVariables->advanceTimeStep()`.
1. reloading `sol` via `GridVariables->init(sol)`;
Codes:
```c++
GridVariables->update(sol);
GridVariables->advanceTimeStep();
```
```c++
GridVariables->init(sol)
```
#### Problems
-[ ] We have to be careful with the initialization of the solvers.
-[x] We have to be careful with the initialization of the solvers.
-**Valid case** Heat solver starts: The heat solver computes a temperature to be send, the heat flux is zero. Thus, the temperature equals the temperature in the cell center.
-**Invalid case** Flow solver starts: The flow solver computes a heat flux from its temperatures. However, the temperature on the interface (stored in the precice adapter) is zero! Thus, a **very high** heat flux is initialized.
-[ ] The implicit coupling creates a solution that develops too fast.
-[x] How do we control the adaptive time stepping? It increases above the suggested time step size which makes it impossible for preCICE to catch the solvers.
-**Note**: There were some errors in the preCICE configuration file.
- [x] The implicit coupling creates a solution that develops too fast.
-**Needs more testing** The checkpointing die only reload parts of the solution. In the end the Newton solver continued from its previous state, but with the initial guess being reset.
- [x] How do we control the adaptive time stepping? It increases above the suggested time step size which makes it impossible for preCICE to catch the solvers.
- I have adapted the adaptive solver. I hope it works properly now!
