[Users] SimulationTools Frequency

[Ian Hinder]

On 6 May 2017, at 08:49, Gwyneth Allwright <allgwy001 at myuct.ac.za> wrote:

> Hi Ian,
> 
> I've been finding SimulationTools very useful for looking at the results of my Cactus simulations. I just have a question about the function called "Frequency", which is used in the context of gravitational waveforms. How is this frequency defined? Is it an angular frequency? I don't know how to interpret the negative values I'm getting.

Hi Gwyneth,

There is actually some documentation for SimulationTools.  You can get the brief usage message for Frequency by typing

	?Frequency

in the notebook.  This tells you:

	Frequency[d] returns the first derivative of the complex phase of d.

That's maybe not as detailed as it could be.

So, if d is a DataTable of complex numbers (i.e. representing a list of {t, f(t)} pairs), Frequency[d] is the time derivative of arg f(t).  

So yes, it is an angular frequency.  The reason it is negative is probably because the orbital angular velocity is positive, and the dominant GW emission is proportional to Exp[-2 I omOrb t].  So omGW = - 2 omOrb.  Usually I plot - Frequency[h].

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

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