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[Johan Hake <question153591@xxxxxxxxxxxxxxxxxxxxx>]

Question #153591 on DOLFIN changed:
https://answers.launchpad.net/dolfin/+question/153591

Johan Hake posted a new comment:
Sorry for late reply:

Try with:

 class cellcoords(Expression):
        def __init__(self, mesh):
                self.mesh = mesh
 	def eval_cell(self, out, x, ufc_cell):
                dolfin_cell = Cell(self.mesh, ufc_cell.index)
                p = dolfin_cell.midpoint()
 		out[0] = x[0]-p.x
 		out[1] = x[1]-p.y
 		out[2] = x[2]-p.z
 	def value_shape(self):
 		return (3,)


Johan

On Wednesday April 20 2011 06:24:29 B. Emek Abali wrote:
> New question #153591 on DOLFIN:
> https://answers.launchpad.net/dolfin/+question/153591
> 
> I need the coordinates relative to the middle of the cell in my form, so I
> came to the idea of
> 
> class cellcoords(Expression):
> 	def eval(self, out, x):
> 		out[0] = x[0]-self.??().midpoint()
> 		out[1] = x[1]-self.??().midpoint()
> 		out[2] = x[2]-self.??().midpoint()
> 	def value_shape(self):
> 		return (3,)
> 
> x = cellcoords()
> 
> where my lack of programming knowledge restricts me to the question marks !
> I dig in the Mesh...h but could not find out..
> 
> How can I reach to a method (midpoint() )  in MeshEntity class from the
> Expression (I think self. directs me to the MeshData class) ?
> 
> any other method is also welcome.
> 
> Thanks a lot,

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