Re: IC files

From: Jay Billings <jayjaybillings_at_gmail.com>
Date: Mon, 14 Sep 2009 07:25:43 -0400

Dimitry,

It is also rather trivial to "invert" the read_snapshot.c file found in the
"Analysis" directory. One benefit of doing it like this is that you have
both read and write routines for Gadget2.

Jay

On Mon, Sep 14, 2009 at 1:19 AM, Dimitry Ayzenberg
<dayzenbe_at_andrew.cmu.edu>wrote:

>
> Thank you very much. That helps a lot. I'm actually using Gadget to try to
> do planet formation simulations, so I'll probably mess with the initial
> conditions on my own. Just needed to know how to actually access them.
>
> Dimitry
>
>
> On Mon, September 14, 2009 01:10, Scott Wales wrote:
> >
>
> > Hi Dimitry,
> >
> >
> > Gadget initial condition files have the same format as snapshots. They
> > are binary files, so you'll have to write a program to actually do
> anything
> > with them. The file format is detailed in the user's guide, but briefly
> > the file consists of a series of blocks, each of which consist of an int
> > containing the block size, a binary blob of data and then another int
> with
> > the block size. Fortran will read the blocks automatically with a
> > unformatted read, for c use a function like
> >
> > #include <assert.h>
> > #include <stdio.h>
> > void ReadGadgetBlock(FILE* gadgetfile, void ** data, size_t * data_size){
> > unsigned int block_size; size_t number_read; // Get the size of the block
> > number_read = fread(&block_size,1,sizeof(block_size),gadgetfile);
> > assert(number_read == 1); // Allocate space for the data
> > *data_size = block_size;
> > *data = realloc(*data,*data_size);
> > // Read the data
> > number_read = fread(*data,*data_size,1,gadgetfile); assert(number_read ==
> > *data_size);
> > // Read the block footer
> > number_read = fread(&block_size,1,sizeof(block_size),gadgetfile);
> > assert(number_read == 1); assert(block_size == *data_size); }
> >
> >
> > The contents of each block are detailed in the user's guide.
> >
> >
> > The initial conditions you'll use depends on what you're simulating.
> > For cosmological simulations try something like Edwin Sirko's ic
> > (needs some format conversion) or Crocce et al.'s 2lpt. They will
> > require input power spectra, found by something like cmbeasy or cmbfast.
> >
> > Cheers,
> >
> >
> > Scott Wales
> >
> >
> > On 14/09/2009, at 2:40 PM, Dimitry Ayzenberg wrote:
> >
> >
> >>
> >> Can someone please tell me how to open and read the .dat files in
> >> the ICs folder? Also how to make initial condition files? I'm a little
> >> confused about how to do either.
> >>
> >> Thanks,
> >> Dimitry
> >>
> >>
> >>
> >>
> >>
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> >>
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> >
> >
> >
> >
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> >
> >
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> >
> >
>
>
> --
> Dimitry Ayzenberg
> Carnegie Mellon University
> Physics - Class of 2012
> Cell:(732)-425-4534
> Email: dayzenbe_at_andrew.cmu.edu
>
>
>
>
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Received on 2009-09-14 13:25:44

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