Re: [deal.II] Accessing nodal values of a FEM solution

2020-07-25 Thread Xuefeng Li
On Fri, Jul 24, 2020 at 9:58 PM Wolfgang Bangerth wrote: > On 7/23/20 12:07 PM, Xuefeng Li wrote: > > > > Well, the above function calculates the gradients of a finite element at > the > > quadrature points of a cell, not at the nodal points of a cell. > > Such a need arises in the following

Re: [deal.II] Accessing nodal values of a FEM solution

2020-07-24 Thread Wolfgang Bangerth
On 7/23/20 12:07 PM, Xuefeng Li wrote: Well, the above function calculates the gradients of a finite element at the quadrature points of a cell, not at the nodal points of a cell. Such a need arises in the following situation. for ( x in vector_of_nodal_points )   v(x) = g(x, u(x), grad

Re: [deal.II] Accessing nodal values of a FEM solution

2020-07-24 Thread Xuefeng Li
On Thu, Jul 23, 2020 at 5:14 PM Daniel Arndt wrote: > > You can do similarly, > > Quadrature q(fe.get_unit_support_points()); > FEValues fe_values (..., q, update_q_points); > for (const auto& cell) > ... > points = fe_values.get_quadrature_points(); >

Re: [deal.II] Accessing nodal values of a FEM solution

2020-07-23 Thread Daniel Arndt
> > We need to update function v based on solution u in the following loop. > > for ( x in vector_of_nodal_points ) > v(x) = f(x, u(x)) > > where v(x) and u(x) are the nodal point value for functions v and u, > respectively, and f() is some function depending on function u as well as > the

Re: [deal.II] Accessing nodal values of a FEM solution

2020-07-23 Thread Xuefeng Li
On Thu, Jul 23, 2020 at 12:43 PM Daniel Arndt wrote: > However, I have two more related questions. BTW, I am a newbie in C++ >> programming. So my questions may seem absurd. >> >>1. Now that we have a vector holding all nodal point coordinates, and >>another vector holding all nodal

Re: [deal.II] Accessing nodal values of a FEM solution

2020-07-23 Thread Daniel Arndt
> > However, I have two more related questions. BTW, I am a newbie in C++ > programming. So my questions may seem absurd. > >1. Now that we have a vector holding all nodal point coordinates, and >another vector holding all nodal point values of the solution. How do we >access every

Re: [deal.II] Accessing nodal values of a FEM solution

2020-07-23 Thread Xuefeng Li
On Sun, Jul 19, 2020 at 7:36 PM Wolfgang Bangerth wrote: > On 7/19/20 6:28 PM, Daniel Arndt wrote: > > > > The tutorial examples show only how to access values of the solution > at > > the quadrature points within each cell. > > > > >

Re: [deal.II] Accessing nodal values of a FEM solution

2020-07-19 Thread Wolfgang Bangerth
On 7/19/20 6:28 PM, Daniel Arndt wrote: The tutorial examples show only how to access values of the solution at the quadrature points within each cell. https://github.com/dealii/dealii/wiki/Frequently-Asked-Questions#how-to-get-the-mapped-position-of-support-points-of-my-element

Re: [deal.II] Accessing nodal values of a FEM solution

2020-07-19 Thread Daniel Arndt
Is it possible to access nodal point values of a solution in deal.ii? And > is it possible to revise nodal values of a solution pointwise? > Yes, of course, the elements of your solution vector correspond to degrees of freedoms which are nodal values in your case. You simply access them (both for

[deal.II] Accessing nodal values of a FEM solution

2020-07-19 Thread Xuefeng Li
Hi, there! I have some general questions about deal.ii, and here is the background info concerning my question. There are two functions u and v, defined over domain \Omega in 1D/2D/3D. We use deal.ii to solve for the numerical approximation of function u, using 1st degree polynomial for