Re: Boxsize of 3 Mpc simulates EXACTLY the same regions as Boxsize = 10 Mpc

From: Tiago Castro <>
Date: Thu, 8 Jul 2021 11:44:53 +0200

Dear Hassan,

   By exactly, I will assume that you mean that by visual inspection, they
look alike, right? For such a small box, the initial power spectrum is
close to a power law for both of them and the initial phases will basically
set the structure formation. If you keep the seed and number of particles,
you are sampling the phases with respect to the box size in the same way.
To run a sub-set of a box, you have to guarantee that the phases are
distributed spatially (and not with respect to the box size) the same way.
In fact, this operation is not simple.

I hope I understood and answer your question.
Kind Regards,
Em qui., 8 de jul. de 2021 às 10:54, Hassan Fathivavsari <>
> Dear all,
> I have changed the BoxSize in the param.txt file in
> the /examples/DM-L50-N128 folder
> to BoxSize = 10 Mpc and ran the simulation.
> I then changed the BoxSize to BoxSize = 3 Mpc and ran the simulation again.
> When I compare the snapshots of the two simulations, I see that they
> represent
> the same regions with the same structures, sub structures, ... etc.
> But I expected the simulation with BoxSize = 3 to represent only a
> sub-section
> of the simulation with BoxSize = 10. But this is not the case and the two
> simulations
> almost exactly look like each other (with some minor variations).
> I would be grateful for any clarification in this issue.
> Many thanks.
> Best regards,
> Hassan
Received on 2021-07-08 11:45:32

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