For the numerical integration of reaction terms in my PDE on a 2D triangular mesh, I would like to use the scheme $$\int_T \Phi(x) \approx \frac{|T|}{3} (\Phi(x_0) + \Phi(x_1) + \Phi(x_2))$$ where the $x_i$ are the triangle nodes.

How to specify this when assembleing the system?

Actually you don't specify quadrature rule to assembler but to form compiler. You can tweak ffc/quadrature_schemes.py for your needs or you can adjust generated code. In both cases you just supply your quadrature points and weights.

• Luckily, assemble() has an form_compiler_parameters argument. – Nico Schlömer May 17 '13 at 13:25
• @Nico: Yes, but FFC seems to accept only default and canonical which is a scheme supplied by FIAT. – Jan Blechta May 17 '13 at 13:28
• Indeed, quadrature_schemes.py doesn't seem to permit custom schemes. – Nico Schlömer May 17 '13 at 13:55