[Users] Compile question

[Ian Hinder]

On 3 Feb 2017, at 00:34, Guy <guy.pitman at bigpond.com> wrote:

> By pointer I meant the path to the KrancExample SimpleWave was added at the end of the Thornlist
> 
> echo 'KrancNumericalTools/GenericFD
> KrancExamples/SimpleWave' >> kranc.th
> I can understand that this compiles this Example , together with some required thorns.

Yes.  The thornlist is a file containing a list of the thorns to include in the configuration.  



> 
>>> Without knowing what all of the individual thorns are doing, is there a risk that
>>> the thornlist that I made up for my Kranccode example (which I did by gradually adding groups of thorns based on error messages) could be incompatible?  
>> I think I'm not following.  What are you trying to achieve?  If you want to follow along the Kranc tutorial, then you only need the thornlist in that tutorial; you shouldn't need any extra thorns.  Since Cactus doesn't compile out-of-the-box on Mac OS, the only change you should need to make is to compile with simfactory instead of with make.  This doesn't mean using the einsteintoolkit.th thornlist; you would still use the thornlist from the tutorial.  For example, you could replace
>> 
>> make kranc-config THORNLIST=kranc.th PROMPT=no
>> 
>> with
>> 
>> sim build kranc --thornlist kranc.th
>> 
> I  guess I am trying to understand the relationship between Kranc thorns as in the examples and other thorns - now that I know where to look for the latter I will probably be able to work it out - presumably it only makes sense to combine certain combinations of thorns , and the example Kranc thorns require specific thorns to be present, but if you add others in to the Thornlist this may change behaviour.

Yes.

> I am trying to understand how one would go about building a new simulation combining existing thorns and new Kranc thorns that would work together.  For example would it make sense to combine more than one Kranc thorn in the thornlist?

Absolutely; Cactus is extremely modular.  Note that just because a thorn is in the thornlist, and hence in the executable, that doesn't mean that it will be activated at runtime.  That depends on the parameter file.  The parameter file that you give to cactus described which thorns to activate (the ActiveThorns lines), and those are the ones that run as part of the simulation.  Usually, a large number of thorns are needed.  For example, there will probably be a thorn to set initial data, another to evolve the equations, and maybe some thorns to compute analysis quantities. Depending on the application, these may all be in one thorn, or they may be distributed.  For example, for a binary black hole evolution, the TwoPunctures thorn computes the initial data, ML_BSSN evolves the metric, and WeylScal4 computes the gravitational radiation via Psi4.  Both ML_BSSN and WeylScal4 are actually Kranc thorns.

-- 
Ian Hinder
http://members.aei.mpg.de/ianhin

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