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

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

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

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

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

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

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