# random function

Asked by Achim Schroll on 2010-03-25

why does my random function return just zero?

from dolfin import *
from random import *

# random funtion
class myrand(Function):
def __init__(self, V):
Function.__init__(self, V)
def eval(self, values, x):
values[0] = gauss(0,1)

# Create mesh and finite element
mesh = UnitSquare(20, 20)
V = FunctionSpace(mesh, "CG", 1)

randf = myrand(V)

## Question information

Language:
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Status:
Solved
For:
DOLFIN Edit question
Assignee:
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Solved by:
Achim Schroll
Solved:
2010-03-25
Last query:
2010-03-25
2010-03-25
 Johan Hake (johan-hake) said on 2010-03-25: #1

Achim!

Just change Function -> Expression and you are good to go!

Johan

On Thursday March 25 2010 05:21:34 Achim Schroll wrote:
> New question #105494 on DOLFIN:
>
> why does my random function return just zero?
>
> from dolfin import *
> from random import *
>
> # random funtion
> class myrand(Function):
> def __init__(self, V):
> Function.__init__(self, V)
> def eval(self, values, x):
> values[0] = gauss(0,1)
>
> # Create mesh and finite element
> mesh = UnitSquare(20, 20)
> V = FunctionSpace(mesh, "CG", 1)
>
> randf = myrand(V)

 Achim Schroll (achim-simula-deactivatedaccount) said on 2010-03-25: #2

Hi Johan, I don't get it. Expression gives the error...

class myrand(Expression):
def eval(self, values, x):
values[0] = gauss(0,1)

mesh = UnitSquare(20, 20)
V = FunctionSpace(mesh, "CG", 1)

randf1 = myrand(V)

Traceback (most recent call last):
File "addnoise_ny.py", line 37, in <module>
randf1 = myrand(V)
File "/usr/lib/python2.5/site-packages/dolfin/expression.py", line 120, in __init__
raise TypeError, "Expression need to be initialized using either a 'cpp.FunctionSpace', using kwarg 'V', or an 'ufl.FiniteElement' using kwarg 'element'."
TypeError: Expression need to be initialized using either a 'cpp.FunctionSpace', using kwarg 'V', or an 'ufl.FiniteElement' using kwarg 'element'.

 Achim Schroll (achim-simula-deactivatedaccount) said on 2010-03-25: #3

it's ok, I got it now - sorry!

 Johan Hake (johan-hake) said on 2010-03-25: #4

Hi again!

Sorry for the incomplete answer. In dolfin 0.9.4 I think you have to pass the
Function space using the keyword argument V=V when you instantiate your
Expression.

randf1 = myrand(V=V)

It's actually there in the error message ;)

In later dolfin version you only need to instantiate your Expression using

randf1 = myrand()

Johan

On Thursday March 25 2010 08:33:48 Achim Schroll wrote:
> Question #105494 on DOLFIN changed:
>
>
> Achim Schroll is still having a problem:
> Hi Johan, I don't get it. Expression gives the error...
>
> class myrand(Expression):
> def eval(self, values, x):
> values[0] = gauss(0,1)
>
> mesh = UnitSquare(20, 20)
> V = FunctionSpace(mesh, "CG", 1)
>
> randf1 = myrand(V)
>
> Traceback (most recent call last):
> File "addnoise_ny.py", line 37, in <module>
> randf1 = myrand(V)
> File "/usr/lib/python2.5/site-packages/dolfin/expression.py", line 120,
> in __init__ raise TypeError, "Expression need to be initialized using
> either a 'cpp.FunctionSpace', using kwarg 'V', or an 'ufl.FiniteElement'
> using kwarg 'element'." TypeError: Expression need to be initialized using
> either a 'cpp.FunctionSpace', using kwarg 'V', or an 'ufl.FiniteElement'
> using kwarg 'element'.