Volume of a mesh and subdomains in c++

Question

How can I find the volume of a dynamic mesh. I'm try to find the volume of a mesh at different time steps. I've define my UFL file as:

element = FiniteElement("Lagrange", tetrahedron, 3)

v = Coefficient(element)
M = 1*dx

FFC gives the error "*** FFC: Expecting a UFL form file (.ufl)."

Comments

How do I translate this for use in C++ via a UFL file:

assemble(1*dx(mesh)) # Volume of entire mesh
assemble(1*dx(0, domain=mesh, subdomain_data=cell_function)) # volume of subdomain 0

Answer 1

You could do something like:

a = CellVolume(tetrahedron)

A = a * dx

forms = [A]

Compile that UFL, and then in c++ assemble A into a double to get the total volume.

Answer 2

Hi gennadiy, It seems like the error is indicating that your UFL file didn't have the .ufl extension. Can you post the full file, including the name?

Dave

Comments

Hi David,

I managed to compile a UFL file as:

Volume.ufl

v = Constant("tetrahedron")
M = v*dx

Then I can supply the constant v as 1 from the C++ file. If I change the UFL to the below, it doesn't compile:

Volume.ufl

M = 1*dx

It gives the error

Compiling form Volume

Compiler stage 1: Analyzing form(s)

*** FFC: 'NoneType' object has no attribute 'label'
*** FFC: To get more information about this error, rerun FFC with --verbose.