It's possible to represent second derivatives in a form, such as assemble(div(grad(f))*dx).  I assume this is true in FEniCS as well as Firedrake, because this is just UFL/FFC/FIAT functionality.  This would produce the sum (over cells) of the Laplacian of f on each cell.

However, like FEniCS, none of our function spaces have more than C^0 continuity.  That is, the functions are at most continuous, but won't have continuous derivatives.  It's likely that you won't want to use second derivatives of C^0 functions in a practical discretisation (though I'm sure there are methods that *do* do this).

Andrew

On 17 July 2015 at 01:50, Justin Chang <jychang48@gmail.com> wrote:

Hi everyone,

Is it possible to do second derivatives? What I mean by that is things like div[grad[u]] and grad[grad[u]]. I haven't tried this out yet, but we use these discretizations a lot for our research, and FEniC's inability to do this made us sad (although our more major qualms had to do with its inability to support quads).

Thanks,

Justin