[Gmsh] Warning: jac < 0

[Aleksejs Fomins]

Dear GMSH,

I have a relatively simple .geo geometry of a prism with curved edges
with several thin layers of stuff on it. When I attempt to make 2nd
order curvilinear mesh from it, it complains that several elements have
negative jacobians. When I visualise this mesh with my own code, I see
that those elements are self-intersecting.

Could someone suggest what is the cause of such behaviour, and what
steps in design I should follow in order to avoid it.

Kind regards,
Aleksejs