Dear Mohammed, Probably your reconstruction involves a (probably local) solve in which case you can do anything that you can express in UFL as a surface integral. If you really need to compute the flux as a separate step then we have trace finite element spaces that you can use. all the best --cjc ________________________________ From: firedrake-bounces@imperial.ac.uk <firedrake-bounces@imperial.ac.uk> on behalf of Mohammad Sarraf Joshaghani <m.sarraf.j@gmail.com> Sent: 14 September 2020 08:01 To: firedrake <firedrake@imperial.ac.uk> Subject: [firedrake] Is it possible to calculate a flux value on the edges of a cell in Firedrake? Hello, I appreciate if you help me with this question. I am trying to implement a postprocessing flux-limiting scheme for a DG advection problem to eliminate the under/overshoots that appears in the vicinity of the front. In order to achieve this, I need to iterate over each mesh element and then on each facet of the element calculate the value of numerical flux. Based on the sign of this Flux value, a constant edge-specific alpha is calculated and the new corrected solutions are then reconstructed for the cell. In firedrake, Is there any way to iterate over facets of each cell, and calculate an integral of an expression (e.g, avg(inner(grad(sol,n))) ) on that facet? This is how I achieved it in fenics: ----------------------------------------------------- facet_domains = MeshFunction('size_t',mesh,mesh.topology().dim()-1) dS = Measure('dS', subdomain_data = facet_domains) elnum = 0 for cell in cells(mesh): flux=np.zeros(3) for fct in facets(cell): flux[fct.index] = assemble( (avg(inner(grad(sol) , n) ) )*dS(fct.index()) print(flux) . . do some operations based on flux[fct.index] values . . elnum += 1 -------------------------------------------------------- Thanks, Sarraf