RE: [deal.II] Re: How to get the shape_value at the quadrature point in the reference cell?

Michael Li Sat, 11 Sep 2021 08:45:18 -0700

Hi Dear Thang,

Thank you for you code snippet! It is simple and works well and is what I want. The link helps me understand the shape function in deal.ii.

Have a good weekend!

Michael

From: Thang W Pham
Sent: Saturday, September 11, 2021 12:20 AM
To: deal.II User Group
Subject: [deal.II] Re: How to get the shape_value at the quadrature point in the reference cell?

Hi Michael,

I think you should have a look at FE_Q (Lagrange elements) at this link. In deal.II, the reference cell's domain is [0,1]^2 for 2d element. So, the point you are about to evaluate (to get the value of phi_i equal 0.25) is (0.5, 0.5).
You can refer to this snippet:

const FE_Q<2> Q_2d_element(1);

const Point<2> center(0.5, 0.5);

for(int i=0; i<Q_2d_element.n_dofs_per_cell(); i++){

std::cout << Q_2d_element.shape_value(i, center) << std::endl;

}

//output 0.25 0.25 0.25 0.25

Also have a look at step-3 to understand how FE_Q works in real problem since the shape functions will be evaluated at real cell coordinates. Good luck.

Regards,

T.P

Vào lúc 07:48:35 UTC+9 ngày Thứ Bảy, 11 tháng 9, 2021, lian...@gmail.com đã viết:

Deal deal.ii comunity,

I want to require the value of a shape function at some quadrature point. But the following code throws an error saying finite_element_output is protected.
double shape_value = fe_values.finite_element_output.shape_values(i, q_index);

For a 2D bilinear element, I expect the shape values at the cell center(kesi=0, eta=0) are 0.25 for all the 4 shape functions.

Is there other way to acquire this information?

Best,
Michael

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RE: [deal.II] Re: How to get the shape_value at the quadrature point in the reference cell?

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