[Nauty] Getting Started with Nauty

[Brendan McKay]

Thanks Gordon.

For larger sizes,  "gentreeg 10 | linegraphg"  will be more efficient.

Saul: The reason your program crashed is that you can't convert
between the dense and sparse types just by casting the pointer type.
Casting pointers in C never changes the object which the pointer
points to.

If you really need to do it inside a program, your choices are:

(1) Write your own procedure to make the linegraph from the
dense graph structure that geng gives you.
(2) Use procedure nauty_to_sg, in the file nausparse.c, to convert
the dense graph to sparse format before calling linegraph().
(3) Use the OUTPROC feature in gentreeg, see the documentation
in gentreeg.c.  Note that it uses yet another data structure: one
designed to be as efficient as possible for trees.  From that you
can easily make the linegraph in some form convenient to you.

Method (3) is the best option if you want to push the computation
as far as possible.

Brendan.

On 28/4/17 11:08 am, Gordon Royle wrote:
> On the command line
>
> geng -c 10 9 | linegraphg
>
> does your job.
>
>
> On 28 Apr 2017, at 8:25 am, Saul Spatz <saul.spatz at gmail.com<mailto:saul.spatz at gmail.com>> wrote:
>
> I'm a complete newbie.  I'm trying to write program that will call geng to
> generate trees of a given order and compute their line graphs.  I modified
> callgeng.c do construct the trees, and it ran successfully.  Since there
> doesn't seem to be a nauty function to compute the line graphs, I just
> copied the function linegraph from linegraphg.c.  Now my OUTPROC looks like:
>
> void OUTPROC(FILE *outfile, graph *g, int n)
> {    /* This will be called for each graph. */
>     ++counter;
>     sparsegraph h;
>     SG_INIT(h);
>     linegraph( (sparsegraph *) g, &h);
> }
>
> When I run the code, I get the error
>
> callgeng(30563,0x7fff7d2c9300) malloc: *** mach_vm_map(size=2251799813685248)
> failed (error code=3)
> *** error: can't allocate region
>
> Apparently this occurs the first time the line
>     DYNALLOC1(size_t,eno,eno_sz,gnde,"linegraphg");
> is executed.  I have never called SG_INIT for g, because the example shows
> that OUTPROC takes a parameter of type graph*, so I have just cast the
> pointer to (sparsegraph*) when calling linegraph.
>
> Is this the source of the problem?  Is there a built-in way to construct a
> sparsegraph from a dense graph?
>
> Thanks for any assistance you can give me.
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> Gordon Royle
>
> School of Mathematics and Statistics
> University of Western Australia
>
> Email: gordon.royle at uwa.edu.au<mailto:gordon.royle at uwa.edu.au>
>
> (Note: my gordon at maths.uwa.edu.au<mailto:gordon at maths.uwa.edu.au> address is deprecated and will stop working soon.)
>
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