if we are making a code of neumann problem “-laplacian u=f on omega , del u/del n =0 on del omega”.
In order to get unique solution we have to impose additional constraint " integral u over omega dx =0 “. how this condition we will impose in weak formulation in fenics.
please provide the idea of the code for " a and l” for the above problem.

sir similar to singular poisson equation code, this is the stokes equation code with additional constraint “integral over omega tr(sig)=0” . then please check is correct. i think their is some error in

"Create vector that spans the null space and normalize" part. here, sig is a stress matrix so tr(sig) is simply the trace of stress matrix. please recorrect my syntax. provide some hint to resolve this problem.

V = VectorElement("Lagrange", mesh.ufl_cell(), 1)
T = TensorElement("Lagrange", mesh.ufl_cell(), 1)
TH = V * T
W = FunctionSpace(mesh, TH)

This is the stokes equation code with additional constraint “integral over omega tr(sig)=0” . As, tr(sig) is simply the trace of stress matrix and it is not a vector component. how we can impose our additional constraint.

Sir can we use quadrature rule in fenics in order to impose the condition that is integral over omega (p) dx =0 in weak formulation if yes then how we can impose…