Impose initial value for control variables in mixed element funciton space

1

I’m solving a problem where I have two variables that I optimize simultaneously. I would like to initialize them to two different values, respectively. I use Dolfin 2019. In my code, I do:

import dolfin
import ufl

v1 = FiniteElement("Lagrange", mesh.ufl_cell(), 1)
v2 = FiniteElement("R", mesh.ufl_cell(), 0)
ME = MixedElement([v1, v2])
FS = FunctionSpace(mesh, ME)

ini_val = Expression(("X0", "X1"), degree=1, X0=4.0, X1=0.5)
interpolate(ini_val, FS)

Which does not output any error, but doesn’t seem to work.
Can anyone let me know what’s not working?

2

It does output error with your code. For example, you do not provide mesh. And based on the context, you should

from dolfin import *

rather than

The function interpolate returns a Function, see API: https://fenicsproject.org/olddocs/dolfin/2019.1.0/python/_autogenerated/dolfin.cpp.function.html?highlight=interpolate#dolfin.cpp.function.interpolate

Consider the following:

from dolfin import *

mesh = UnitSquareMesh(4, 4)

v1 = FiniteElement("Lagrange", mesh.ufl_cell(), 1)
v2 = FiniteElement("R", mesh.ufl_cell(), 0)
ME = MixedElement([v1, v2])
FS = FunctionSpace(mesh, ME)
F  = Function(FS)

ini_val = Expression(("X0", "X1"), degree=1, X0=4.0, X1=0.5)
f = interpolate(ini_val, FS)
f1, f2 = f.split()
# Or
F.assign(f)
print(F.vector()[:])
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