# Data exchange during sub-iteration of implicit coupling

**URL:** <https://precice.discourse.group/t/data-exchange-during-sub-iteration-of-implicit-coupling/2306>\
**Category:** Using preCICE\
**Tags:** adapters\
**Created:** [January 16, 2025, 6:36am UTC](https://precice.discourse.group/t/data-exchange-during-sub-iteration-of-implicit-coupling/2306 "2025-01-16T06:36:15Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![smjo1021](https://yyz2.discourse-cdn.com/free1/user_avatar/precice.discourse.group/smjo1021/32/2412_2.png) [@smjo1021](https://precice.discourse.group/u/smjo1021)\
**Post date:** [January 16, 2025, 6:36am UTC](https://precice.discourse.group/t/data-exchange-during-sub-iteration-of-implicit-coupling/2306/1 "2025-01-16T06:36:15Z")

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Hello preCICE team,

I am using preCICE for volume couplings of two solvers. Implicit coupling is used to simulate unsteady motion of system of interest. I wonder if data exchange during the sub-iteration of the implicit coupling is feasible or not. For example, if the implicit coupling dt is 1e-3 s, and I want to make 20 sub-iterations between each dt marching, is it allowed by preCICE to let the codes exchange the data during the 20 sub-iterations? I was trying to dig the tutorial case of FSI, but could not figure out this yet. Any comments/notes will be extremely helpful.

Sincerely,

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**Author:** ![Makis](https://yyz2.discourse-cdn.com/free1/user_avatar/precice.discourse.group/makis/32/25_2.png) [@Makis](https://precice.discourse.group/u/Makis)\
**Post date:** [March 19, 2025, 5:40pm UTC](https://precice.discourse.group/t/data-exchange-during-sub-iteration-of-implicit-coupling/2306/2 "2025-03-19T17:40:29Z")

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Hi @smjo1021,

sounds to me what you are looking for is the time interpolation feature: [Waveform iteration for time interpolation of coupling data | preCICE - The Coupling Library](https://precice.org/couple-your-code-waveform.html)

This does not do what you ask for, but probably does what you want to achieve.

@BenjaminRodenberg would be the expert to ask regarding this.

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**Author:** ![fsimonis](https://yyz2.discourse-cdn.com/free1/user_avatar/precice.discourse.group/fsimonis/32/6_2.png) [@fsimonis](https://precice.discourse.group/u/fsimonis)\
**Post date:** [June 3, 2025, 2:30pm UTC](https://precice.discourse.group/t/data-exchange-during-sub-iteration-of-implicit-coupling/2306/3 "2025-06-03T14:30:28Z")

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In short

- data exchange happens at the end of the time window
- there can be multiple iterations per time window
- doing multiple substeps produces samples
- samples can be used for time interpolation (piece-wise linear by default) in the next iteration of the same time window

Hope that helps