# About internal state when using implicit coupling
**URL:** https://precice.discourse.group/t/about-internal-state-when-using-implicit-coupling/1822
**Category:** Using preCICE
**Tags:** checkpointing
**Created:** [March 10, 2024, 8:19am UTC](https://precice.discourse.group/t/about-internal-state-when-using-implicit-coupling/1822 "2024-03-10T08:19:03Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@ilovenili](https://precice.discourse.group/u/ilovenili)
#### Post date: [March 10, 2024, 8:19am UTC](https://precice.discourse.group/t/about-internal-state-when-using-implicit-coupling/1822/1 "2024-03-10T08:19:03Z")
HI:
when I read the precice literature named “Efficient and Flexible Partitioned Simulation of Fluid-Structure Interactions” , in section 2.3.2, I can’t understand the words follow:
I think it’s very important to understand implicit, so who can help me interpretate it?(i think give a example is the best!)
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### Author:  [@Makis](https://precice.discourse.group/u/Makis)
#### Post date: [March 11, 2024, 7:47pm UTC](https://precice.discourse.group/t/about-internal-state-when-using-implicit-coupling/1822/2 "2024-03-11T19:47:34Z")
> [@ilovenili](#):
>
> Efficient and Flexible Partitioned Simulation of Fluid-Structure Interactions
You are reading Bernhard Gatzhammer’s dissertation from 2014. You might find more related resources in our literature guide:
> **[Literature guide | preCICE - The Coupling Library](https://precice.org/fundamentals-literature-guide.html)**
>
> A guide to the main reference literature for each component and feature of preCICE
However, the first place I would look at would be the current and official documentation:
> **[Coupling scheme configuration | preCICE - The Coupling Library](https://precice.org/configuration-coupling.html)**
>
> The coupling scheme is the centerpiece of the preCICE configuration. It describes the logical execution order of two or more participants. On this page, we explain how to couple two participants.
Put simply, `implicit coupling` means that there is an “external loop”: solvers don’t only exchange information once (`explicit coupling`), but repeatedly, until the information on their interface converges.
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### Author:  [@ilovenili](https://precice.discourse.group/u/ilovenili)
#### Post date: [March 12, 2024, 1:35am UTC](https://precice.discourse.group/t/about-internal-state-when-using-implicit-coupling/1822/3 "2024-03-12T01:35:57Z")
yes, but for “the two possibilities how the internal state is teated” ,This statement shows that there is a clear difference between these two approaches to implicit coupling, but what is the difference?
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### Author:  [@Makis](https://precice.discourse.group/u/Makis)
#### Post date: [March 12, 2024, 7:19am UTC](https://precice.discourse.group/t/about-internal-state-when-using-implicit-coupling/1822/4 "2024-03-12T07:19:28Z")
Ah, I see now what you are asking. This pretty much describes the following:
- Option A: I can control when to “advance” the solver state to the next time step. If preCICE tells me that the coupling is complete, then I advance the solver state to the next time step.
- Option B (more common): I cannot control how the solver advances in time. For this reason, I keep checkpoints, and I force the solver to go back in time and repeat the computation of some time steps.
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### Author:  [@ilovenili](https://precice.discourse.group/u/ilovenili)
#### Post date: [March 13, 2024, 1:32am UTC](https://precice.discourse.group/t/about-internal-state-when-using-implicit-coupling/1822/5 "2024-03-13T01:32:59Z")
ok，very clear，thanks!
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### Author:  [@system](https://precice.discourse.group/u/system)
#### Post date: [March 16, 2024, 1:33am UTC](https://precice.discourse.group/t/about-internal-state-when-using-implicit-coupling/1822/6 "2024-03-16T01:33:43Z")
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