[SOLVED] Conditional value of function

Thanks Martin Sandve Alnæs, that solved my question.

Thanks Martin for the quick answer.

One further thought : is there a way to define a function which would be able to handle some more intricate conditions ?
Writing becomes quite unhandy after a few combined ones.
Thanks,
Michael

Hi Michael, I have had luck using something like:

r = 1
C = 2
class fun(Expression):
    def eval(self, values, x):
        if numpy.sqrt((x[0]-cx)**2+(x[1]-cy)**2) < r:
            values[0] = 1+C
        else:
            values[0] = 1

Then fun() is an expression which equals 3 on the unit disk and 1 outside. Using interpolate(fun(),V), with V being a FunctionSpace you get the corresponding Function.

As you can see, you can simply define the fun() as you wish using the coordinates x[0],x[1],x[2] and define the values[0] as the output.

Hi Henrik ,
Thank you for answering.
I was actually looking for defining the values of a Function dependently from the values of another one, and not just from the coordinates. I don't know if there have been some significant advances lately but UFL manual from 2010 states :

TODO: This is rather limited, probably need the operations ”and” and ”or”
as well, the syntax will be rather convoluted... Can we improve? Low priority
though.
[Advanced] Because of details in the way Python behaves, we cannot over-
load the builtin comparison operators for this purpose, hence these named
operators.

Check out the UFL chapter in the FEniCS book instead. It's available online
through fenicsproject.org somewhere.

On 31 October 2012 16:35, Michael Bruckner <
<email address hidden>> wrote:

> Question #212669 on FEniCS Project changed:
> https://answers.launchpad.net/fenics/+question/212669
>
> Michael Bruckner posted a new comment:
> Hi Henrik ,
> Thank you for answering.
> I was actually looking for defining the values of a Function dependently
> from the values of another one, and not just from the coordinates. I don't
> know if there have been some significant advances lately but UFL manual
> from 2010 states :
>
> TODO: This is rather limited, probably need the operations ”and” and ”or”
> as well, the syntax will be rather convoluted... Can we improve? Low
> priority
> though.
> [Advanced] Because of details in the way Python behaves, we cannot over-
> load the builtin comparison operators for this purpose, hence these named
> operators.
>
> --
> You received this question notification because you are a member of
> FEniCS Team, which is an answer contact for FEniCS Project.
>

Example:
C syntax: (u < 0.5 && u > -0.5) ? 1.0: 0.0
UFL syntax: conditional( And( lt(u, 0.5), gt(u, -0.5) ), 1.0, 0.0 )

On 31 October 2012 16:56, Martin Sandve Alnæs <email address hidden> wrote:

> Check out the UFL chapter in the FEniCS book instead. It's available
> online through fenicsproject.org somewhere.
>
>
> On 31 October 2012 16:35, Michael Bruckner <
> <email address hidden>> wrote:
>
>> Question #212669 on FEniCS Project changed:
>> https://answers.launchpad.net/fenics/+question/212669
>>
>> Michael Bruckner posted a new comment:
>> Hi Henrik ,
>> Thank you for answering.
>> I was actually looking for defining the values of a Function dependently
>> from the values of another one, and not just from the coordinates. I don't
>> know if there have been some significant advances lately but UFL manual
>> from 2010 states :
>>
>> TODO: This is rather limited, probably need the operations ”and” and ”or”
>> as well, the syntax will be rather convoluted... Can we improve? Low
>> priority
>> though.
>> [Advanced] Because of details in the way Python behaves, we cannot over-
>> load the builtin comparison operators for this purpose, hence these named
>> operators.
>>
>> --
>> You received this question notification because you are a member of
>> FEniCS Team, which is an answer contact for FEniCS Project.
>>
>
>

Thanks Martin, this is how I got it working.