rtabmap_ros: how it works?

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Hi to all,

I'm using the rtabmap_ros package in my project in order to build 3D maps from my recorded bags files. The package works very well and I'm able to obtain accurate maps.

I've read all the documents about the RTAB-Map algorithm and also the articles wrote by Mathieu Labbé. The problem is that I still can't understand how mathematically the closed loop detection works and how the 3D map is built.

Is there any document which I can read in order to understand how the algorithm mathematically works? Can you help me please?

Thank you a lot!