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## Fem-fenics

, 07:13, 16 September 2013
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=== Mixed Formulation for Poisson Equation ===
In this example the poisson equation is solved with a mixed approach: the stable FE space obtained using Brezzi-Douglas-Marini polynomial of order 1 and Dicontinuos element of order 0 is used.

$-\mathrm{div}\ ( \mathbf{\sigma} (x, y) ) ) = f (x, y) \qquad \mbox{ in } \Omega$

$\sigma (x, y) = \nabla u (x, y) \qquad \mbox{ in } \Omega$

$u(x, y) = 0 \qquad \mbox{ on } \Gamma_D$

$(\sigma (x, y) ) \cdot \mathbf{n} = \sin (5x) \qquad \mbox{ on } \Gamma_N$

A complete description of the problem is avilable on the [http://fenicsproject.org/documentation/dolfin/1.2.0/python/demo/pde/mixed-poisson/python/documentation.html Fenics website.]
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