DOLFIN

create Function from MeshFunction / CellFunction ?

Asked by Paul Constantine on 2013-02-02

Is it possible to create a Function from a MeshFunction or CellFunction? I have a function defined by points in a text file. I can create a CellFunction following the example on page 189 of the FEniCS book. But I want to use this like a Function. Is such a thing possible? Can I go directly from the text file to a Function via something like project()? I couldn't find anything like this in the demos or the examples in the book.

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DOLFIN Edit question
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Solved by:
Paul Constantine
Solved:
2013-02-02
Last query:
2013-02-02
Last reply:
Paul Constantine (paul-g-constantine) said : #1

Okay, something like this works, but it seems a little clunky. Let me know if you know anything slicker.

====
from dolfin import *
from numpy import loadtxt,interp

class MySine(Expression):

    def __init__(self,filename):
        self.data = loadtxt(open(filename,"rb"),delimiter=",",skiprows=1)

    def eval(self,values,x):
        values[0] = interp(x[0],self.data[:,0],self.data[:,1])

if __name__ == "__main__":

    f = MySine("sine_file.txt")

    mesh = UnitIntervalMesh(10)
    V = FunctionSpace(mesh,"CG",1)
    fV = project(f,V)

    print fV(0.33)
    print f(0.33)

====

Garth Wells (garth-wells) said : #2

Take a look at

    demo/undocumented/tensor-weighted-poisson/

for an example.

Paul Constantine (paul-g-constantine) said : #3

Looks great! Thanks!