Constraint nodes value

Hi,

I am a beginner at Fenics. Is there any way to set up a constraint condition for the nodes? I am testing with a basic heat conduction problem. and created a simple bifurcation mesh:

editor.add_vertex(0, np.array([0.0,0.0,0.0]))
editor.add_vertex(1, np.array([0.0279,0,0]))
editor.add_vertex(2, np.array([0.0279,0.0,0]))
editor.add_vertex(3, np.array([0.043032,0.015132,0]))
editor.add_vertex(4, np.array([0.0279,0.0,0]))
editor.add_vertex(5, np.array([0.043032,-0.015132,0]))

editor.add_cell(0, np.array([0,1], dtype=np.uintp))
editor.add_cell(1, np.array([2,3], dtype=np.uintp))
editor.add_cell(2, np.array([4,5], dtype=np.uintp))

Is that possible to set a constrain that node1=node2+node4?

Many Thanks!

That is a multi point constraint and has been implemented as an add on to dolfin-x. See:

And

Note that you are constraining degrees of freedom (located at vertices). In dolfin and dolfinx the mesh and function space is decoupled. This means that you can have an arbitrary order function space on a first order geometry

Thank you very much
I will take a look