Re: [deal.II] ABOUT ASSEMBLING RIGHT HAND SIDE
Dear Wolfgang, Thank you very much. I will try to see what happened by myself. Best, Xiang On Wednesday, 8 April 2020 10:46:04 UTC-7, Wolfgang Bangerth wrote: > > On 4/8/20 10:20 AM, 孙翔 wrote: > > > > I tried the zero boundary and it can get a correct answer. I truly used > the > > function for the matrix once in a time loop. In the new time loop, I > have > > updated the system matrix and vector. I am trying to debug it. Could you > help > > me review the code? If it is a stupid mistake, please just tell me it is > and I > > will try to continue to debug it. If it is due to some function usage or > > mathematics, please help me with some details because I am just a > beginner and > > really want to learn more from dealii. > > I can't debug everyone's code here on this mailing list, I'm afraid. I had > a > brief look and the setup of the system matrix looks correct/reasonable to > me. > But then you describe that you have two methods of which one works and the > other doesn't, and I don't know what this program implements; I also don't > know what the *expected* solution for this program is. So I'm afraid > you'll > have to discuss this yourself. But as in the last few days, I'm happy to > provide ideas for how to debug. You'll just have to do it yourself... > > Best > W. > > -- > > Wolfgang Bangerth email: bang...@colostate.edu > > www: http://www.math.colostate.edu/~bangerth/ > > -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to dealii+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/a7ab689e-9684-4d00-8e8f-7003a1948c75%40googlegroups.com.
Re: [deal.II] ABOUT ASSEMBLING RIGHT HAND SIDE
On 4/8/20 10:20 AM, 孙翔 wrote: I tried the zero boundary and it can get a correct answer. I truly used the function for the matrix once in a time loop. In the new time loop, I have updated the system matrix and vector. I am trying to debug it. Could you help me review the code? If it is a stupid mistake, please just tell me it is and I will try to continue to debug it. If it is due to some function usage or mathematics, please help me with some details because I am just a beginner and really want to learn more from dealii. I can't debug everyone's code here on this mailing list, I'm afraid. I had a brief look and the setup of the system matrix looks correct/reasonable to me. But then you describe that you have two methods of which one works and the other doesn't, and I don't know what this program implements; I also don't know what the *expected* solution for this program is. So I'm afraid you'll have to discuss this yourself. But as in the last few days, I'm happy to provide ideas for how to debug. You'll just have to do it yourself... Best W. -- Wolfgang Bangerth email: bange...@colostate.edu www: http://www.math.colostate.edu/~bangerth/ -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to dealii+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/d44e2125-f86a-f4c9-a2dc-b4de61b83261%40colostate.edu.
Re: [deal.II] ABOUT ASSEMBLING RIGHT HAND SIDE
On 4/7/20 5:31 PM, 孙翔 wrote: I applied a Dirichlet boundary condition after I formed system matrixes and vectors, then use the method you taught in the lecture to change the entries in the system matrix and rhs vector. Could I upload the code here in order to make it clear? You can, but you will have to learn to debug these problems yourself. If the boundary values are wrong, is this the case if the correct boundary values are nonzero? Does it also happen if the correct boundary are zero? If it works for zero boundary values, then you should carefully read step-26 again: You can only use apply_boundary_values() once for a given matrix because it changes the matrix. Best WB -- Wolfgang Bangerth email: bange...@colostate.edu www: http://www.math.colostate.edu/~bangerth/ -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to dealii+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/f91c4e60-60e3-2db9-3cb2-564c6da42d62%40colostate.edu.
Re: [deal.II] ABOUT ASSEMBLING RIGHT HAND SIDE
Hi, Wolfgang, I applied a Dirichlet boundary condition after I formed system matrixes and vectors, then use the method you taught in the lecture to change the entries in the system matrix and rhs vector. Could I upload the code here in order to make it clear? Thank you very much. Best, Xiang On Tuesday, 7 April 2020 16:03:10 UTC-7, Wolfgang Bangerth wrote: > > On 4/7/20 4:58 PM, 孙翔 wrote: > > > > Do you mean the Dirichlet boundary condition? I applied the boundary > condition > > after I form the right-hand side vector. I don't think the boundary > condition > > will lead to different solutions because the right-hand side vector has > been > > different before I add the boundary conditions. > > "I don't think" is the wrong approach :-) You are seeing something you are > not > expecting. In other words, what you "expect" is not happening, and so you > need > to let go of what you think is happening -- you need to *verify* that what > you > think is happening is happening! That's the whole mind set of debugging > problems :-) > > Best > WB > > > -- > > Wolfgang Bangerth email: bang...@colostate.edu > > www: http://www.math.colostate.edu/~bangerth/ > > -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to dealii+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/13771a9b-4ee7-4a7e-91b7-e763ab0917a9%40googlegroups.com.
Re: [deal.II] ABOUT ASSEMBLING RIGHT HAND SIDE
Hi, Wolfgang, Thanks a lot. I didn't apply refinement in my code, so there is no hanging node problem. As you said, there is a big difference around the boundary. I set the boundary value always equal to the initial value which is equal to 1. The M*old_solution method gives the correct answer which is 1, but the second method can not. The attached file is the solution. Best, Xiang On Tuesday, 7 April 2020 16:03:10 UTC-7, Wolfgang Bangerth wrote: > > On 4/7/20 4:58 PM, 孙翔 wrote: > > > > Do you mean the Dirichlet boundary condition? I applied the boundary > condition > > after I form the right-hand side vector. I don't think the boundary > condition > > will lead to different solutions because the right-hand side vector has > been > > different before I add the boundary conditions. > > "I don't think" is the wrong approach :-) You are seeing something you are > not > expecting. In other words, what you "expect" is not happening, and so you > need > to let go of what you think is happening -- you need to *verify* that what > you > think is happening is happening! That's the whole mind set of debugging > problems :-) > > Best > WB > > > -- > > Wolfgang Bangerth email: bang...@colostate.edu > > www: http://www.math.colostate.edu/~bangerth/ > > -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to dealii+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/89db432f-1bbc-436a-a14c-c79b71d887a1%40googlegroups.com.
Re: [deal.II] ABOUT ASSEMBLING RIGHT HAND SIDE
On 4/7/20 4:58 PM, 孙翔 wrote: Do you mean the Dirichlet boundary condition? I applied the boundary condition after I form the right-hand side vector. I don't think the boundary condition will lead to different solutions because the right-hand side vector has been different before I add the boundary conditions. "I don't think" is the wrong approach :-) You are seeing something you are not expecting. In other words, what you "expect" is not happening, and so you need to let go of what you think is happening -- you need to *verify* that what you think is happening is happening! That's the whole mind set of debugging problems :-) Best WB -- Wolfgang Bangerth email: bange...@colostate.edu www: http://www.math.colostate.edu/~bangerth/ -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to dealii+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/a5dac54b-9e2a-1f12-db7b-95c52babfd1a%40colostate.edu.
Re: [deal.II] ABOUT ASSEMBLING RIGHT HAND SIDE
Hi, Jean-Paul, Do you mean the Dirichlet boundary condition? I applied the boundary condition after I form the right-hand side vector. I don't think the boundary condition will lead to different solutions because the right-hand side vector has been different before I add the boundary conditions. Best, Xiang On Tuesday, 7 April 2020 13:27:17 UTC-7, Jean-Paul Pelteret wrote: > > Hi Xiang, > > You’ve also not mentioned whether you’re comparing vectors before or after > you’ve distributed the constraints. Perhaps you get the same result if you > call constraints.distribute() on both of your vectors? > > Best, > Jean-Paul > > > On 07 Apr 2020, at 22:22, Wolfgang Bangerth > wrote: > > > > On 4/5/20 12:32 AM, Xiang Sun wrote: > >> For correction, the right code for the second method is > > > [...] > > > > Are you saying that you solved your own problem? Or are you still > unclear what is happening? > > > > Best > > W. > > > > > > -- > > > > Wolfgang Bangerth email: bang...@colostate.edu > > > www: http://www.math.colostate.edu/~bangerth/ > > > > -- > > The deal.II project is located at http://www.dealii.org/ > > For mailing list/forum options, see > https://groups.google.com/d/forum/dealii?hl=en > > --- You received this message because you are subscribed to the Google > Groups "deal.II User Group" group. > > To unsubscribe from this group and stop receiving emails from it, send > an email to dea...@googlegroups.com . > > To view this discussion on the web visit > https://groups.google.com/d/msgid/dealii/77b269f1-b91b-1dc3-2145-b023242ba43c%40colostate.edu. > > > > -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to dealii+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/dbbae2fe-3a1d-4120-9922-c24463ff5e93%40googlegroups.com.
Re: [deal.II] ABOUT ASSEMBLING RIGHT HAND SIDE
Hi Xiang, You’ve also not mentioned whether you’re comparing vectors before or after you’ve distributed the constraints. Perhaps you get the same result if you call constraints.distribute() on both of your vectors? Best, Jean-Paul > On 07 Apr 2020, at 22:22, Wolfgang Bangerth wrote: > > On 4/5/20 12:32 AM, Xiang Sun wrote: >> For correction, the right code for the second method is > > [...] > > Are you saying that you solved your own problem? Or are you still unclear > what is happening? > > Best > W. > > > -- > > Wolfgang Bangerth email: bange...@colostate.edu > www: http://www.math.colostate.edu/~bangerth/ > > -- > The deal.II project is located at http://www.dealii.org/ > For mailing list/forum options, see > https://groups.google.com/d/forum/dealii?hl=en > --- You received this message because you are subscribed to the Google Groups > "deal.II User Group" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to dealii+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/dealii/77b269f1-b91b-1dc3-2145-b023242ba43c%40colostate.edu. -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to dealii+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/E8F4F48E-9EE1-48B1-A301-F62441E0698B%40gmail.com.
[deal.II] ABOUT ASSEMBLING RIGHT HAND SIDE
Hi, I am implementing the backward Euler method to solve a time-dependent
problem like u(n+1)= h*f(n+1)+u(n). n is the nth time step. h is the time
step length. f is a function of time. I tried two ways to assemble the
system right-hand side(rhs).
One is to form a mass matrix first, then time the old value of u at the
node. This way is similar to Step-26. The code is like
mass_matrix.vmult(system_rhs, old_solution);
The other way is to get the value of u at quadrature points by
interpolation, then do the integral in cells to get the local rhs, finally
assemble the system rhs by the local rhs. This method is from Step-31 and
shown in the following code.
for (; cell != endc; ++cell) {
local_rhs = 0;
fe_values.reinit(cell);
fe_values.get_function_values(old_solution, old_sol_values);
for (unsigned int q = 0; q < n_q_points; ++q ){
for (unsigned int i = 0; i < dofs_per_cell; ++i) {
const double phi_i = fe_values.shape_value(i, q);
local_rhs(i) += old_sol_values[q] * phi_i * fe_values.JxW(q);
}
}
cell->get_dof_indices(local_dof_indices);
for (unsigned int i = 0; i < dofs_per_cell; ++i) {
system_rhs(local_dof_indices[i]) += local_rhs(i)*0;
}
}
I thought these two methods should give the same answer, but they can't. I
don't know where I made a mistake. Thank you very much.
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