# numerical flux HDG+

1 month 1 week ago #3160
Hi,

I am trying to implement an HDG+ method. I am having trouble with a term involving the L^2projection of an unknown.

For example, for an element K
$u_h \in \mathcal P_{p+1}(K),\quad\mu\in \Pi_{F\in \partial K}\mathcal P_p(F)$
. I would like to compute
$\int_{\partial K} P_{M} uh \mu ds$

where P_M is the L^2 projection onto the space
$\mathcal P_{p+1}(K)$
.

Is possible to implement L^2 projection as operators?

I would appreciate any help.

Thanks.

1 month 1 week ago #3161
Hi Manuel,

To realize the projected jumps, you simply add the flag "highest_order_dc=True" in your facet fe space, and keep the poly degree the same for both volume and facet fespace.
E.g.:
V = L2(mesh, order=4)
M = L2(mesh, order=4, highest_order_dc=True)

The global linear system with such M consists of cubic polynomials on the facet.

Take a look at section 2.2 of this reference.
www.sciencedirect.com/science/article/pii/S004578251630264X

Best,
Guosheng