[Gmsh] High-order quads

[Geordie McBain]

2011/3/16 Martin Vymazal <martin.vymazal at vki.ac.be>:
> Hello,
>
>  could someone please tell me what is the local node numbering for P3
> quadrilaterals in gmsh? Looking in the documentation, it seems that P3 quads
> are not supported, but using "-order 3" I still can generate a mesh with
> elements which look like this:
>
>           x---x---x---x
>           |           |
>           x   x   x   x
>           |           |
>           x   x   x   x
>           |           |
>           x---x---x---x
>
>  Can you please tell me what are the local node numbers?

Hello.  I found this ASCII diagram in a C comment on lines 317--332 of
Geo/MQuadrangle.h.

/*
 * MQuadrangle
 *
 *   3--3+3E-...--4+2E--2
 *   |                  |    E = order - 1;
 *   |                  |    N = total number of vertices
 * 4+3E                3+2E
 *   |                  |    Interior vertex numbers
 *  ...  4+4e to N-1   ...    for edge 0 <= i <= 3: 4+i*E to 3+(i+1)*E
 *   |                  |     in volume           : 4+4*E to N-1
 * 3+4E                4+E
 *   |                  |
 *   |                  |
 *   0---4--...---3+E---1
 *
 */

I think it should specialize to the case you want for E=2, so that,
for example, along the bottom we'd have 0, 4, 5, 1.