Hello there,

I am still relatively new to fenics and am currently trying to apply the weak formulation to nonlinear equations. How do i get to the weak formulation of a poissonlike equation, with a nonlinearity in the source function? For example i would like to solve

\Delta \phi = \rho^2.

With a given \phi, how do i have to formulate this to be able to solve for \rho?

Thank you all in advance.