Re: [Users] running ML_ADMConstraints with timelevels=1 and no SYNCs

[Roland Haas]

Hello Erik, Frank, all,

yes, I would only compute and output the constraints on the coarse
level timestep.

> The largest issue I see is that e.g. a regular L2 norm over the simulation
> domain is not very useful. It emphasizes very much the coarse grid, which
> is very large, and where the boundary conditions might do strange things to
> the constraints. Similarly, you will need to be careful to exclude the
> interior of the horizons (see CarpetMask) to avoid looking near the
> punctures. CarpetMask is not smooth in time, so looking at the time
> evolution of the constraint norm is then also problematic.
CarpetMask is active and set up (Ian had thankfully already pointed
this out).

> You might be more happy if you look e.g. at the "isum" or "inorm2" output.
> This output is not weighted by coordinate volume, but by grid cells, so
> that the coarse grid is deemphasized.
Ok, I will add isum and inorm2 to the output.Currently I had norm_inf,
norm1 and norm2. Really these are only intended to check for obvious
errors in the parameter file the make the contraints grow.

Yours,
Roland

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Re: [Users] running ML_ADMConstraints with timelevels=1 and no SYNCs

[Erik Schnetter]

The ghost and buffer zones are also used for time interpolation, but since
you suggest to only evaluate the constraints when the coarse level is
active, you are circumventing this.

The largest issue I see is that e.g. a regular L2 norm over the simulation
domain is not very useful. It emphasizes very much the coarse grid, which
is very large, and where the boundary conditions might do strange things to
the constraints. Similarly, you will need to be careful to exclude the
interior of the horizons (see CarpetMask) to avoid looking near the
punctures. CarpetMask is not smooth in time, so looking at the time
evolution of the constraint norm is then also problematic.

You might be more happy if you look e.g. at the "isum" or "inorm2" output.
This output is not weighted by coordinate volume, but by grid cells, so
that the coarse grid is deemphasized.

-erik


On Thu, Sep 22, 2016 at 9:14 PM, Roland Haas  wrote:

> Hello all,
>
> I am wondering if there would be anything wrong with running
> ML_ADMConstraints with just a single time level for the constraints as
> well as using no SYNCs for it as long as I set it's calc_every
> parameter to the frequency of the coarsest level.
>
> Obviously this will give my "nonssense" values in the ghost zones,
> buffer zones and boundary (though on the boudary I can just set it to
> zero).
>
> However since the constraints are pure output and nothing ever depends
> on them the bad values only matter if they were to eg show up in the
> norms. It is my recollection that CarpetReduce actually does not use
> any values from the ghost zones (certainly that would be wrong) or
> buffer zones (this may be more recent).
>
> Is there any any other way the "bad" values could make it into the
> norms? Note that I do not worry about 1d, 2d, 3d output for the
> constraints.
>
> Yours,
> Roland
>
> --
> My email is as private as my paper mail. I therefore support encrypting
> and signing email messages. Get my PGP key from http://keys.gnupg.net.
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Erik Schnetter 
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[Users] running ML_ADMConstraints with timelevels=1 and no SYNCs

[Roland Haas]

Hello all,

I am wondering if there would be anything wrong with running
ML_ADMConstraints with just a single time level for the constraints as
well as using no SYNCs for it as long as I set it's calc_every
parameter to the frequency of the coarsest level.

Obviously this will give my "nonssense" values in the ghost zones,
buffer zones and boundary (though on the boudary I can just set it to
zero). 

However since the constraints are pure output and nothing ever depends
on them the bad values only matter if they were to eg show up in the
norms. It is my recollection that CarpetReduce actually does not use
any values from the ghost zones (certainly that would be wrong) or
buffer zones (this may be more recent). 

Is there any any other way the "bad" values could make it into the
norms? Note that I do not worry about 1d, 2d, 3d output for the
constraints.

Yours,
Roland

-- 
My email is as private as my paper mail. I therefore support encrypting
and signing email messages. Get my PGP key from http://keys.gnupg.net.


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