Re: How to set up the number of particle

From: Sander Valcke <>
Date: Mon, 26 Oct 2009 09:40:00 +0100

Hi Feng-Yin,

the number of particles in an initial conditions file is set in the that
files header. Look in the manual at page 29+, there you can see the
structure of a Gadget-2 snapshot. Table 4 shows you the precise content
of the header, with Npart[6] containing the number of particles of each
type in that file.

How to change the number of particles depends on the IC generator you
are using. It should typically ask you for the number of particles of
each/some type(s) you want to set up. It then enters those numbers into
the snapshot header + generate positions, velocities, ... for the
required number of particles and adds those to the snapshot.

kind regards,

Sander wrote:
> Hi everyone,
> I'm just a beginner to use Gadget-2 and now trying hard on understanding
> the code.
> I've run the example of lcdm-gas.param provided by Gadget but only known
> the number of particle
> when reading out the snapshot. Has the number of particle been set in
> initial condition?
> Recently, I found the website of the PiTP summer school this year on
> computational astrophysics.
> There are several exercises for Gadget-2. I used N-GenIC to generate the
> initial condition, however
> I couldn't find any input about the number of particle. In the parameter
> file (ics.param), only Nmesh and Nsample
> were set up. However the exercise one asked us to simulate LambdaCDM
> cosmology with particle 128^3 or 64^3
> for shrinking the time. How can I reduce the number of particle?
> Thanks,
> Feng-Yin Chang
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| Sander Valcke                                  |
| Sterrenkundig Observatorium, Universiteit Gent |
| Krijgslaan 281 S9, B-9000 Gent, Belgium        |
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|       |
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Received on 2009-10-26 09:59:44

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