Typically, when solving a classical problem like the Laplace equation, we may construct the matrix A starting from the bilinear form, build the right-hand side b and solve the system using A^(-1)*b. When the matrix A is sparse there is no problem. However, if some non-local terms are in the bilinear form, the matrix of the bilinear form may be full so I would like to avoid constructing it.

On the other hand, constructing a function which computes A*v where v is a vector is quite efficient in my case. Is there a functionality in FreeFEM which allows to solve a system of equations A*x=b if instead of the matrix A we have a function computing the product A*v for an arbitrary v? (I know such a functionality exists for Eigenvalue problems, but I cannot find it quickly in the documentation for a linear system).