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Re: [Getfem-users] interface condition question

 From: Jehanzeb Hameed Subject: Re: [Getfem-users] interface condition question Date: Thu, 9 Jul 2009 16:18:30 -0500

```Hello,

I am now comfortable enough with getfem to start attacking the
interface problem, thanks to help from this list. In the code for
getfem++/contrib/inter_element_test, there is piece of code which I
cant fully understand, and I havent been able to figure it from the
documentation. The relevant lines of code are:

const base_matrix& B = ctx1.B();
gmm::mult(B, pgt1->normals()[f1], up);
scalar_type norm = gmm::vect_norm2(up);
scalar_type J = ctx1.J() * norm;

What is the matrix B? Also, does J give the determinant of Jacobian
transformation for the face (if so, why)?

Also, on a related note, I am planning to use the technique in this
file to implement the jump integral. Yves mentioned the method in
crack.cc, which uses mortars and some sort of constraints matrix,
which I havent looked into yet. Is there a reason to prefer one of the
two approaches?

Thanks,
-Jehanzeb

> Hello,
>
> it was not fully straightforward but you can find an example in:
> getfem++/contrib/inter_element_test,
> if you have matching meshes on the interface. If not it is certainly
> possible but I am not the expert to explain how to do.
>
> I hope it helps,
> Best regards,
> Ronan
>
> Jehanzeb Hameed a écrit :
>>
>> Hello,
>>
>> I am investigating the possibility of using getfem for implementing a
>> 2 domain problem, with an interface between the domains. I want to use
>> continuous lagrange elements on each domain, and a jump condition at
>> the interface. The jump condition will take the form (u_1 - u_2, v_1 -
>> v_2), where u_1 and v_1 and test and trial functions for domain 1, and
>> u_2 and v_2 are test and trial functions for domain 2.  The integral
>> (u_1 - u_2, v_1 - v_2) is only over the interface between the domains.
>>
>> Can this be done relatively easily in getfem?
>>
>> Thanks,
>> -Jehanzeb
>>
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