ise constant element (P1). The expected convergence rate is 2nd order in H(div) and L2 norm for $\sigma$ and L2 norm of $u$.</p>
<p><strong>References</strong>
See page 12, Table 9.2. Arnold, Douglas N. and Falk, Richard S. and Winther, Ragnar. Geometric decompositions and local bases for spaces of finite element differential forms. Comput. Methods Appl. Mech. Engrg. 198():1660--1672, 2009.</p>
<p><strong>Subroutines</strong>:</p>

<pre><code>- PoissonRT1
- squarePoissonRT1
- mfemPoisson
- PoissonRT1mfemrat