Hassan
Thorn RotatingSymmetry90 assumes Cartesian coordinates; it will not help you. Thorn Periodic is the right thorn to use, with one periodic direction, e.g. y, just as you did.
What exactly is going wrong? One has to be careful with the number of grid points, number of boundary points, and whether the boundary is on or in between grid points. Here is my first attempt:
I assume you use 3 ghost zones, that you want to have a grid point at phi=-pi (and at phi=+pi), and that you want to have a grid spacing of 2pi/36 in the phi direction:
# How we want to specify things CoordBase::domainsize = "minmax" CoordBase::spacing = "numcells"
# This is the easy part CoordBase::ymin = -3.14... CoordBase::ymax = +3.14... CoordBase::ncells_y = 36 # Similarly for x and z
# Now the meticulous grid point counting CoordBase::boundary_size_y_lower = 3 # 3 boundary points, since there are 3 ghost points CoordBase::boundary_size_y_upper = 3 CoordBase::boundary_shiftout_y_lower = 1
The last line is probably difficult to guess. It means that the point at the lower boundary (at y=-pi) is not a boundary point; the boundary begins only one gridpoint below. This means that this gridpoint is evolved in time. Conversely, the point at y=+pi is a boundary point; it is not evolved in time, since it is set via the periodicity condition. This means that the points y=-pi and y=+pi are treated differently – this may be confusing at first, but is actually correct, since your domain is in this case [-pi; +pi), i.e. the lower boundary is included while the upper boundary is not.
The thorn CoordBase has some documentation with figures that explain these parameters.
Note that the number of cell in the phi direction needs to be even if you want a grid point at phi=0.
-erik
On Tue, Mar 1, 2011 at 3:47 PM, Seyyed Mohammad Hassan Halataei smhhalataei@gmail.com wrote:
Dear Erik,
Thank you for your respond. I want to use cylindrical coordinates in my problem (r, phi, z) and I think I need a physical boundary condition for phi ,rather than a symmetry. It seems rotational boundary condition can be helpful and I thought if I use periodic boundary condition for phi (namely , periodic_y = yes) the code should satisfy my demand . However, it could not.
Am I on the right track ? I think RotatingSymmetry90 cannot do that , because I want to have the full range [-PI, PI] and evolve it . All I need is connecting two ends of the grid in phi direction (or y) together . In other words, I like to tape -PI to PI.
Do you think the thorn Periodic is the appropriate thorn or there is a better thorn which can do that for me ?
Thank you Hassan
On Mon, Feb 28, 2011 at 5:37 PM, Erik Schnetter schnetter@cct.lsu.edu wrote:
Hassan
The current version of this thorn is located in an svn repository at http://svn.cactuscode.org/arrangements/CactusNumerical/Periodic. However, this thorn implements a toroidal symmetry, not a rotational symmetry. Can you describe the symmetry that you are trying to apply? For example, there is another thorn CactusNumerical/RotatingSymmetry90 that may be more suitable. There is also another thorn available that implements a Cartoon symmetry.
We describe much of our code at http://einsteintoolkit.org, and we use the mailing list users@einsteintoolkit.org for discussion. Would you mind using this mailing list instead of keeping this conversation private? The mailing list has the advantage that others will also be able to help when I don't know the answer.
-erik
On Mon, Feb 28, 2011 at 6:20 PM, halatae1@illinois.edu wrote:
Dear Dr. Schnetter,
I am Hassan Halataei, working in Professor Shapiro's Numerical Relativity group in Univ. of Illinois at Urbana-Champaign. I am trying to use the thorn Periodic you have written in 2003 to implement rotational symmetry in my problem (Single Black hole surrounded by an accretion disk) . I read the 2-page documentary of the thorn and acted according to that . However, the thorn does not work for me . I tried several different things for days to make it work , however the result does not obey periodic boundary condition . I was wondering if you let me know if there is anything that I missed or any other consideration that I must take care of ?
Thank you Hassan
-- Erik Schnetter schnetter@cct.lsu.edu http://www.cct.lsu.edu/~eschnett/