Is Cartographer result consistent?

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Hi, I have run the cartographer slam with the same bag file multiple times.

There is a small variance among all the map results. (YES, I compared the occupied grid map)

Is the variance normal?

(I understand that the the Gmapping has variance because of the feature of Particle Filter. And the Hector has a consistent result since it uses Gaussian-Newtown for scan matching (with the same input data the Gaussian-Newtown gives the consistent result.))

So, what is the theory behind the Cartographer map variance?

Thank you