====== Saving and Restoring an Array of Polytopes ======

If you want to deal with a whole family of polytopes at the same time, it will sometimes be convenient to save and restore them to a single file. polymake has a simple mechanism for this, storing your array of polytopes into a single tarball.

The necessary functions for this are contained in the script "tarballs" that you can load into your polymake session by calling

<code perl>
> script("tarballs");
</code>
It provides the two functions ''%%pack_tarball%%'' and ''%%unpack_tarball%%''.

===== Storing =====

Here is a simple example, where we create an array @a containing a cube and a simplex and save this to a file.

<code perl>
> @a = ();
> $a[0] = cube(3);
> $a[1] = simplex(3);
> pack_tarball("simple_polytopes.tgz",@a);
</code>
This creates a file ''%%simple_polytopes.tgz%%'' in the current directory that is a tarred (and gzipped) archive containing two polymake files. polymake detects whether you want the archive gzipped or not from the supplied file extension (''%%*.tar.gz%%'' or ''%%*.tgz%%''). You can verify this by calling ''%%tar tvfz simple_polytopes.tgz%%'' from the command line:

<code>
[nightingale]:~/temp>tar tvfz simple_polytopes.tgz 
-rw------- xxx/yyy 1468 2009-07-01 17:20 1.poly
-rw------- xxx/yyy  854 2009-07-01 17:20 2.poly
[nightingale]:~/temp>
</code>
If you want to get more descriptive names for your polymake files then you have to set a name for each polytope first.

<code perl>
> $a[0]->name = "my_cube";
> $a[1]->name = "my_simplex";
> pack_tarball("simple_polytopes.tgz",@a);
</code>
sets the names of the files in the tarball to ''%%my_cube.poly%%'' and ''%%my_simplex.poly%%'':

<code>
[nightingale]:~/temp>tar tvfz simple_polytopes.tgz 
-rw------- xxx/yyy  952 2009-07-01 17:21 my_cube.poly
-rw------- xxx/yyy  650 2009-07-01 17:21 my_simplex.poly
[nightingale]:~/temp>
</code>
===== Restoring the array =====

You can restore your saved array by using the function ''%%unpack_tarball%%'':

<code perl>
> @a=unpack_tarball("simple_polytopes.tgz");
> print $a[0]->name;
my_cube

</code>
If you just want a specific polytope from your tarball, then you can supply its name in the command:

<code perl>
> @a=unpack_tarball("simple_polytopes.tgz","my_simplex.poly");
> print $a[0]->name;
my_simplex

</code>
You may supply more than one filename. However, wildcards are not supported. Note that changes in the files are not automatically stored in the archive, you have to call ''%%pack_tarball%%'' to update the files.

===== Packing archives outside polymake =====

You can of course apply ''%%tar%%'' to your favorite family of polymake files to create a tarball without using polymake. It can be read by polymake as long as the files are at the root of the archive (i.e. don't pack a whole directory tree). The archive also may not contain non-polymake files.