3.3.2 Nonlinear diffusion problem

Assume that we want to solve the Bratu equation -\Delta u = e^u on the unit square \Omega=(0,1)^2 with Dirichlet boundary conditions u(x,y)=0 for (x,y) \in \partial \Omega. The following command solves this equation approximately on a uniformly refined mesh using as termination criterion that the time for approximating the solution has increased beyond 20 seconds.

(storing (solve (blackboard :problem (bratu-problem 2) 
                            :success-if '(> :time 20) :output :all)))

Again, the result of the call to solve is a blackboard which is saved in the global variable *result* for later reference. It is interesting to study the actual definition of the Bratu problem in the function bratu-problem.