getfem-users
[Top][All Lists]

## Re: [Getfem-users] interface condition question

 From: Renard Yves Subject: Re: [Getfem-users] interface condition question Date: Sun, 12 Jul 2009 13:20:03 +0200 User-agent: Dynamic Internet Messaging Program (DIMP) H3 (1.1)

```
Jehanzeb Hameed <address@hidden> a écrit :

```
```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)?
```
```
```
B is the transpose of the inverse of the gradient of the geometric transformation (pseudo-inverse if the element have a lower dimension than the mesh) see the documentation pages
```

```
ctx1.J() is the jacobian of the transformation of the whole element. Multiplied by the norm of the normal to the face, it gives the jacobian of the transformation of the face, yes.
```
```
```
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?
```
```
```
It depends of what you need to do. If you have a single mesh with to regions and a discontinuity between the two regions, the faster is probably the method used in crack.cc.
```

Regards,

Yves.

```
```
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

_______________________________________________
Getfem-users mailing list
https://mail.gna.org/listinfo/getfem-users

```
```

```
```
_______________________________________________
Getfem-users mailing list
```