[firedrake] defining an expression piecewise

[Colin Cotter]

Hi Francis,
  What is the function space you are using?

You can build a piecewise constant function using the C-string Expression
via the ?: ternary operator in C.

all the best
--cjc

On 26 February 2017 at 22:05, Francis Poulin <fpoulin at uwaterloo.ca> wrote:

> Hello,
>
> I am trying to define an expression piecewise and see that I need to do
> that by defining a class.    Below is something that I tried, building on
> what I read, but it has an error, see below.
>
> class MyExpression(Expression):
>     def eval(self, value, x):
>         if x[0] <= 0.5:
>             value[0] = 1.0
>         else:
>           value[0] = 0.0
>
>     def value_shape(self):
>         return (1,)
>
> f.interpolate(MyExpression())
>
> It fails with the following error:
>
> AttributeError: 'FunctionSpace' object has no attribute 'interpolate'
>
>
> Can someone maybe point me in the right direction on how to do tis
> properly?
>
> Cheers, Francis
>
> ------------------
> Francis Poulin
> Associate Professor
> Department of Applied Mathematics
> University of Waterloo
>
> email:           fpoulin at uwaterloo.ca
> Web:            https://uwaterloo.ca/poulin-research-group/
> Telephone:  +1 519 888 4567 x32637 <(519)%20888-4567>
>
>


-- 
http://www.imperial.ac.uk/people/colin.cotter

www.cambridge.org/9781107663916
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