# MED Volume and boundary connectivities

All,

I created a square mesh with one QUAD4 or QUAD9 element to understand the connectivity in the .med file

and the corresponding boundary connectivity of SEG2 or SEG3.

For the boundary connectivity I get the list "1 1 3 2 2 3 4 4" which I don't understand how I should interpret.

In fact, an edge cannot be described by two node indices that are the same, so I don't know how to read the edges here.

Also, the connectivity of QUAD4 runs counterclockwise in this case.

Then, I created a mesh with 4 square elements instead, and it seems to me that the QUAD4 connectivity now goes differently,

say "like a cross", and the boundary connectivity seems to be more understandable at least.

Also: if I want to have a biquadratic mesh, do I always have first all the linear connectivities listed, then the added nodes,

or is it something that happens only when I start with a linear mesh and then I use "Convert to biquadratic"?

Is there a way to compute the biquadratic mesh from the beginning, without conversion, and would the connectivity list change in that case?

Thanks for your help,

Giorgio