Anders Logg wrote:
> On Thu, Mar 05, 2009 at 04:55:38PM +0100, Patrick Riesen wrote:
>> hi all
>>
>> i'm stuck on the following problem:
>>
>> i'd like to compute a term as
>>
>> eta = (gamma)^(-2/3), or general eta = gamma^(n) and n is real
>>
>>
>> in my code, gamma is dependent on a velocity function from a previous
>> interation, so gamma = gamma(u0), and how to compute gamma stems from a
>> form-file, so i do:
>>
>> _M_gamma = new gammaFunctional(u0);
>>
>> Function f_gamma(&mesh, *M_gamma, 0);
>>
>>
>> my question is now
>>
>> how can i create the other function f_eta = f_gamma^(2/3) in a nice way?
>>
>> what i thought about is to create a derived function class Eta where
>> overload the evaluation function in a way as
>>
>> double eval(const double* x) const
>> {
>> return (gamma.eval(x)*gamma.eval(x))^(-1/3)
>> }
>>
>> please tell me if this is a possible approach, or else advise me how to
>> handle this :-)
>>
>>
>> thanks a lot for the support,
>>
>> patrick
>>
>> (btw i do this together with dolfin-grade2 so i use dolfin0.8.1 )
>
> I'd suggest operating on the vectors of dofs. Send in the gamma
> function to the constructor of your Function subclass, pick out the
> vector of dofs, iterate over the dofs and just insert the values into
> the vector using pow(x[i], 2.0/3.0).
>
> Use the get/set methods in Vector to first pick out arrays, operate on
> the arrays and then put them back.
>
hi anders,
i understand how to create the f_eta class and hand in the f_gamma but
i'm uncertain on what to do inside f_eta exactly. can you give me some
more help, e.g. in a few pseudocode statements?
thanks a lot for the help,
patrick
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