Finally I had some time to write a basic test example for PCBDDC ( http://petsc.cs.iit.edu/petsc/petsc-dev/rev/848c8bdc7bcb) It illustrates the basic features of MATIS assembling (which to my knowledge was not present in PETSc examples) and BDDC customization by solving a simple Laplacian discretized by the spectral element method with Gauss-Lobatto-Legendre quadrature rule. -- Stefano