Re: [deal.II] Re: Why does the L2-norm increase when the number of nodes becomes too large?

2017-12-21 Thread 'Uwe Köcher' via deal . II User Group
Dear Luca (and Jie) due to your comment On Wednesday, 20 December 2017 17:20:43 UTC+1, Luca Heltai wrote: > > M… > > I’m actually not sure it’s a bug… The point where the error starts growing > is at 10e-12. This is basically machine precision, considering the fact > that you are computing

Re: [deal.II] Re: Why does the L2-norm increase when the number of nodes becomes too large?

2017-12-21 Thread jie liu
Sorry, the coordinate of x axis is the number of nodes, and the coordinate of y axis is L2 error of the variable. Jie -- 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 be

Re: [deal.II] Re: Why does the L2-norm increase when the number of nodes becomes too large?

2017-12-21 Thread jie liu
Hi Praveen, On Thursday, December 21, 2017 at 3:38:21 AM UTC+1, Praveen C wrote: > step-7 uses QGauss(3) to compute error norm. Have you tried increased > number of quadrature points ? > > > Also, what is the quadrature rule you use for assembling? > Yes, I increased the number of quadrature p

Re: [deal.II] Re: Why does the L2-norm increase when the number of nodes becomes too large?

2017-12-20 Thread Praveen C
> On 21-Dec-2017, at 8:04 AM, Praveen C wrote: > > > >> On 20-Dec-2017, at 11:52 PM, jie liu > > wrote: >> >> Hi Luca, >> >> On Wednesday, December 20, 2017 at 5:20:43 PM UTC+1, Luca Heltai wrote: >> >> What’s the tolerance of your solver? Is it a direct or an

Re: [deal.II] Re: Why does the L2-norm increase when the number of nodes becomes too large?

2017-12-20 Thread Praveen C
> On 20-Dec-2017, at 11:52 PM, jie liu wrote: > > Hi Luca, > > On Wednesday, December 20, 2017 at 5:20:43 PM UTC+1, Luca Heltai wrote: > > What’s the tolerance of your solver? Is it a direct or an iterative solver? > If it is an iterative solver, is the tolerance right around 1e-12? > > Th

Re: [deal.II] Re: Why does the L2-norm increase when the number of nodes becomes too large?

2017-12-20 Thread jie liu
Hi Luca, On Wednesday, December 20, 2017 at 5:20:43 PM UTC+1, Luca Heltai wrote: > > What’s the tolerance of your solver? Is it a direct or an iterative > solver? If it is an iterative solver, is the tolerance right around 1e-12? > > Thank you for your reply. I adopted both iterative and direct

Re: [deal.II] Re: Why does the L2-norm increase when the number of nodes becomes too large?

2017-12-20 Thread luca.heltai
M… I’m actually not sure it’s a bug… The point where the error starts growing is at 10e-12. This is basically machine precision, considering the fact that you are computing the L2 error. After you have reached machine precision, any addition you make to that, is just roundoff error addin

[deal.II] Re: Why does the L2-norm increase when the number of nodes becomes too large?

2017-12-20 Thread 'Uwe Köcher' via deal . II User Group
Dear Jie, I'm with Bruno, you definately have a bug in your code. Maybe the application of the Dirichlet boundary is incorrect. When you use the 1d grid generation the left and right boundary nodes are coloured by different numbers. This is a different behaviour compared to 2d or 3d grid genera

[deal.II] Re: Why does the L2-norm increase when the number of nodes becomes too large?

2017-12-19 Thread Bruno Turcksin
Hi, On Tuesday, December 19, 2017 at 2:58:20 PM UTC-5, jie liu wrote: > > > This phenomenon is not desired. Different solvers are adopted, but there > is no improvement on it. Can anybody give some clues? Thank you. > You have a bug in your code. What you should see is that the error decreases a