About the magnitude of the error: I used 24 cells. May be this could be a clue for the bug. I will investigate...
On Tuesday, May 24, 2016 at 8:11:12 AM UTC+2, Praveen C wrote: > > Dear Mauro > > I am getting rather large errors for the integral of div(v) and the other > one. Here is the output > > Running with mappingq > Setting RotatedSphericalManifold > Setting SphericalManifold > Setting RotatedSphericalManifold > Setting SphericalManifold > Setting SphericalManifold > Setting SphericalManifold > Grid has been saved into grid.vtk > Surface mesh has 96 cells. > Surface mesh has 48000 degrees of freedom. > Div integral = 8.68643e-22 > n*v integral = 2.6536e-21 > Surface area = 12.5664 > Relative error in surface area = 3.67531e-15 > > Running with mappingmanifold > Setting RotatedSphericalManifold > Setting SphericalManifold > Setting RotatedSphericalManifold > Setting SphericalManifold > Setting SphericalManifold > Setting SphericalManifold > Grid has been saved into grid.vtk > Surface mesh has 96 cells. > Surface mesh has 48000 degrees of freedom. > Div integral = 4.13656e-09 > n*v integral = 3.24529e-09 > Surface area = 12.6084 > Relative error in surface area = 0.00334306 > > Could you run the attached code and see if you get the same result ? > > Note that these integrals are performed on each cell. The value you see > above is the maximum taken over all cells. If you add the integrals from > all cells, that may be zero due to cancellation on the sphere, but the cell > integrals could still be wrong. Note that integral on each cell must be > zero which is what I am checking in my code. > > Thanks > praveen > > On 24-May-2016, at 3:33 AM, Mauro Bardelloni <[email protected] > <javascript:>> wrote: > > Dear Praveen, > > I noticed that the divergence theorem is safe. :) > > Mapping Manifold: > \int_{\partial K} v \cdot n = -8.51746e-21 > \int_{K} \div v = -3.74547e-21 > Mapping Q: > \int_{\partial K} v \cdot n = -5.70692e-22 > \int_{K} \div v = 3.09366e-21 > > BTW, as you pointed out there is something wrong. I tried to calculate the > surface of a unit sphere: > Mapping Manifold: > Area = 12.7092 > Error = 0.142811 > Mapping Q: > Area = 12.5664 > Error = 9.78773e-12 > > Probably there is an issue in the JxW. I printed it for every cell and I > found that > for the Mapping manifold is: > -> 0.529549 > -> 0.529549 > ... > -> 0.529549 > -> 0.529549 > while for the MappingQ is: > -> 0.523599 > -> 0.523599 > ... > -> 0.523599 > -> 0.523599 > > > > > -- 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 [email protected]. For more options, visit https://groups.google.com/d/optout.
