# about the use of dS

Hello

I am trying to solve the Poisson equation in 2D using

the discontinuous galerkin methode (DG).

\delta (\kappa \delta T) = f

Here I want to use an auxiliary variable

q = \kappa \delta T

It is not working. I include the script I am using.

The CG method works and gives a nive solution. It is not

the case with the DG method.

Probably somebody familiar with this method could

explain me what I am doing wrong. I am learning this

kind of method and trying to make it work with simple

examples.

Thanks a lot!

=======

from dolfin import *

methode = "DG" # CG / DG

# Create mesh and define function space

mesh = UnitSquare(32, 32)

V_q = VectorFunctionS

V_T = FunctionSpace (mesh, methode, 1)

W = V_q * V_T

# Define test and trial functions

(q, T) = TrialFunctions(W)

(w, v) = TestFunctions(W)

# Define mehs quantities: normal component, mesh size

n = FacetNormal(mesh)

# define right-hand side

f = Expression(

# Define parameters

kappa = 1.0

# Define variational problem

if methode == 'CG':

a = dot(q,w)*dx \

+ T*div(kappa*w)*dx \

+ div(q)*v*dx

elif methode == 'DG':

#modele = "IP"

C11 = 1.

a = dot(q,w)*dx + T*div(kappa*w)*dx \

- kappa*avg(

+ dot(q,grad(v))*dx \

- dot( avg(grad(T)) - C11 * jump(T,n) ,n('-'))*v('-')*dS

L = -v*f*dx

# Compute solution

qT = Function(W)

solve(a == L, qT)

# Project solution to piecewise linears

(q , T) = qT.split()

# Save solution to file

file = File("poisson.pvd")

file << T

# Plot solution

plot(T); plot(q)

interactive()

## Question information

- Language:
- English Edit question

- Status:
- Answered

- For:
- DOLFIN Edit question

- Assignee:
- No assignee Edit question

- Last query:
- 2013-05-26

- Last reply:
- 2013-05-27

Jan Blechta (blechta) said : | #1 |

This forum is closed now. For support check http://

Regarding your problem you might be intersted in http://

## Can you help with this problem?

Provide an answer of your own, or ask Dupront for more information if necessary.