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Hello community：
I've noticed that in SU2, data transfer between grids in multi-zone problems only occurs when the two grids share a common boundary. I want to implement a way to transfer information even when there is no shared boundary, which is why I am reading this part of the code.
While reviewing the Interface source code, I noticed that during the Broadcast process, the boundary markers markDonor and markTarget for the Donor and Target are first obtained. This utilizes the FindInterfaceMarker function within the CConfig class.（Figure1) In the definition of this function, there is a principle I don't understand, especially regarding "SideA = Marker_ZoneInterface[2 * iInterface]" and "sideB = Marker_ZoneInterface[2 * iInterface + 1]". I comprehend the latter part of the statement where a judgment is made based on whether "tag = SideA or sideB", and the returned iMarker should belong to either the Donor or the Target and is then stored. However, I am unclear about why SideA and SideB are defined in this manner.
And I would like to inquire further about the conditional statement "if (!CInterpolator::CheckInterfaceBoundary(markDonor, markTarget)) continue". (Figure2)My understanding is that if two zones share a boundary, then the markers of that boundary will be present in all processes. Otherwise, it indicates that the two zones do not share a boundary. If there is no shared boundary, the rest of the loop iteration will not be executed. I would like to ask, if I directly modify this conditional statement, can I also allow the meshes of two zones that do not share a boundary to be processed as well?
Since my grasp of CFD and programming is relatively weak, I have these questions. The question might be a bit lengthy, thank you for your patient reading. Any suggestions for my research are welcome. Thank you for your valuable answers.