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Re: [Getfem-users] second derivative of linear elements
From: |
Yves Renard |
Subject: |
Re: [Getfem-users] second derivative of linear elements |
Date: |
Wed, 12 Feb 2014 12:53:47 +0100 (CET) |
Dear Wen,
interpolator_on_mesh_fem is a structure which mainly allows to use a
precomputed solution to enrich a finite element space. It only interpolate the
solution and its gradient. It is an interpolation, thus the gradient of a P1
function will be constant over an element, yes. If you just need to interpolate
a gradient or a Hessian on a cloud of points, you should preferably use the
functions in getfem_derivatives.h and getfem_interpolation.h but you should
first interpolate the gradient/Hessian on a discontinous finite element on the
same mesh, then use the interpolation function in getfem_interpolation.h to
interpolate on a cloud of points. Of course, it would be possible to provide a
function which performs both the two operations in only one step, but it does
not exist for the moment.
Best regards,
Yves.
----- Original Message -----
From: "Wen Jiang" <address@hidden>
To: address@hidden
Sent: Tuesday, February 11, 2014 11:41:55 PM
Subject: Re: [Getfem-users] second derivative of linear elements
Sorry to clog your inbox. In my previous email I forgot to tell that I used
interpolator_on_mesh_fem to get the gradient and hessian. Basically I would
like the get the first derivative and second derivative of the displacement
field at some points. I understand that the gradient is definitely
discontinuous across elements so we have to use a discontinuous fem as the
targeted fem if the compute_gradient() is used. But I am not sure about how the
gradient and hessian is calculated when calling
interpolator_on_mesh_fem.eval(...) and .eval_hess(...). As I said, if the
linear element is used, are those results still correct? Thanks.
Regards,
Wen
On Tue, Feb 11, 2014 at 9:55 AM, Wen Jiang < address@hidden > wrote:
Dear all,
I tried to calculate the second derivative in getfem using compute hessian. For
linear elements, the second derivative of the shape function should be zero but
it seems that the results of hessian computed in getfem is not zero. Could you
tell me how is the hessian computed in getfem for linear elements? Thanks.
Regards,
Wen
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