Yes, tensor product of Lagrange polynomials, often written as Q_k. Degrees of freedom associated with Dirichlet boundary conditions have been removed in the systems you're looking at.
Yann Jobic via petsc-users <petsc-users@mcs.anl.gov> writes: > Dear Petsc Users, > > I've been playing with the option "space_degree", in 2D, for a space > discretisation of 4 cells (2x2), for a poisson problem, and i wonder > what are the underlying concepts. > > With a space degree 2, i get a 9x9 algebraic system, and i've got a > solution convergence order of 3. > > With a space degree 3, i get a 25x25 algebraic system, and i've got a > solution convergence order of 4. > > So my question is : what are the basis functions associated with each > space degree ? > > Are they lagrange polynomials or something else ? > > Thanks! > > Yann