On 24 Jun 2010, at 09:24, Erik Schnetter wrote:
On Jun 24, 2010, at 1:23 , Ian Hinder wrote:
On 23 Jun 2010, at 14:25, Frank Loeffler wrote:
On Wed, Jun 23, 2010 at 02:06:13PM -0400, Ian Hinder wrote:
I'm confused about what parameters you are talking about. In EinsteinInitialData/TwoPunctures/param.ccl, there is a parameter center_offset[i]. Is this the one you are referring to?
That is right.
We do use this parameter for unequal mass BBH simulations.
I suspected so.
If so, in what way is it broken?
It changes the grid functions x, y and z by that offset. You might be lucky and Carpet might overwrite that before the first time step though.
Do you still get the same results of you comment out the lines around 621 in TwoPunctures.c (the whole loop basically)?
I computed initial data before and after this change and wrote the BSSN conformal factor to HDF5. I then used h5diff to compare the resulting files. There were no differences apart from the build-id and simulation-id. However, the coordinates themselves *do* show differences, which I need to look into in more detail. The only thing I can think of in a BBH simulation which uses the coordinates gridfunctions is wave extraction, as they are often used to compute the tetrad. Are they also used by the interpolator?
No, the coordinate grid functions are only used by initial data. The PUGH and Carpet interpolators assume coordinates that can be expressed as "offset with delta", which is much more efficient than looking at grid functions.
Good!
Since one knows during wave extraction where the extraction sphere is located, the coordinate grid functions are probably also not used there (but this depends on the code). I assume that one would not interpolate coordinates (since this should be an identity), therefore errors in the coordinate grid functions should not matter there either.
Psi4 is a contraction of the Weyl tensor with a tetrad. The components of this tetrad are usually based on the coordinates, and the coordinate gridfunctions are typically used for this (at least in WeylScal4) since this is a pointwise operation at each point in the grid.