Discussion related to cado-nfs

[Paul Leyland <paul.leyland@gmail.com>]

(TL;DR --- having troubles setting up a SNFS factorization with cado-nfs
2.0 beta)


On Thu, 2013-10-24 at 10:06 +0100, Paul Leyland wrote:
> I would like to suggest that the documentation on how to run SNFS with
> CADO-NFS be expanded.  Unless I've missed something very important the
> present documentation can be summarized as "create a polynomial file by
> hand instead of using the GNFS polynomial finder".

Further to this, I'm trying to set up to factor 235*8^235+1 which has
just started under "Msieve v. 1.52 (SVN 923M)".  The msieve polynomial
file, working very nicely, is

        n: 
9344879323330582132476647523076036766251058644308032256575482675551196064229458278655388065516061224981191913520205352585413584634611067426349293720079701
        Y0: -166153499473114484112975882535043072
        Y1: 1
        c0: 1
        c1: 0
        c2: 0
        c3: 0
        c4: 0
        c5: 0
        c6: 1880
        skew: 0.284647271438178
        
and I've saved that as msieve.poly on the system where cado-nfs is
installed

The docs in cado-nfs refer me to:

        Factoring with SNFS:
        ====================
        
        It is possible to take advantage of the special form of an
        integer and use the Special Number Field Sieve. See the doc in
        scripts/cadofactor/parameters.snfs for that.

but that file isn't in the beta tarball ====> documentation bug at
least.

The doc in scripts/cadofactor/README tells me to
        
        If you want to import a polynomial file (either a SNFS
        polynomial, or
        polynomial selection was already done), use:
        
        tasks.polyselect.import=xxx.poly
        
        where xxx.poly is the name of the polynomial file (in CADO-NFS
        format).
        
        By default this will consider this polynomial in addition to
        those found during
        the polynomial selection. If you want to avoid polynomial
        selection, also add:
        
        tasks.polyselect.admin=0
        tasks.polyselect.admax=0

which I did.  After unsuccessful attempts to convert to CADO-NFS format
by hand I discovered /installed/bin/misc/convert_poly which is not
obviously documented.  After experimentation I used 

        convert_poly -if msieve < msieve.poly > c8_235.poly

with the result
        n: 0
        c0: 0
        Y0: 0
        m: 0

which is not very helpful  8-(

Tried again with the msieve c8_235.fb file as input to convert_poly.
The contents this time are

        N
        
9344879323330582132476647523076036766251058644308032256575482675551196064229458278655388065516061224981191913520205352585413584634611067426349293720079701
        SKEW 0.284647271438178
        A6 1880
        A5 0
        A4 0
        A3 0
        A2 0
        A1 0
        A0 1
        R1 1
        R0 -166153499473114484112975882535043072
        FAMAX 26400000
        FRMAX 26400000
        SALPMAX 536870912
        SRLPMAX 536870912
        
with result

        n: 
9344879323330582132476647523076036766251058644308032256575482675551196064229458278655388065516061224981191913520205352585413584634611067426349293720079701
        c6: 1880
        c5: 0
        c4: 0
        c3: 0
        c2: 0
        c1: 0
        c0: 1
        Y1: 1
        Y0: -166153499473114484112975882535043072
        m: 166153499473114484112975882535043072
        
Importing this one (note the SKEW line in the input and lack of a skew:
line in the output) into cado-nfs yielded

        ...
        Info:Client Launcher: Running clients: localhost4 (Host
        localhost, PID 4045), localhost3 (Host localhost, PID 4042),
        localhost2 (Host localhost, PID 4039), localhost (Host
        localhost, PID 4036)
        Info:Polynomial Selection: Starting
        Info:Polynomial Selection: No polynomial was previously found
        Warning:Polynomial Selection: Invalid polyselect file
        '/home/pcl/cado_fact/c8_235.poly': Key skew missing
        Info:Polynomial Selection: Adding workunit
        c8_235_polyselect_0-100000 to database
        Info:Polynomial Selection: Adding workunit
        c8_235_polyselect_100000-200000 to database
        ...

Adding a line

        skew: 0.284647271438178

to c8_235.poly and restarting cadofactor.py produced

        ...
        Info:Client Launcher: Running clients: localhost4 (Host
        localhost, PID 4307), localhost3 (Host localhost, PID 4304),
        localhost2 (Host localhost, PID 4301), localhost (Host
        localhost, PID 4298)
        Info:Polynomial Selection: Starting
        Info:Polynomial Selection: No polynomial was previously found
        Warning:Polynomial Selection: Polynomial in
        file /home/pcl/cado_fact/c8_235.poly has no Murphy E value
        Info:Polynomial Selection: New best polynomial from
        file /home/pcl/cado_fact/c8_235.poly: Murphy E = 0
        Info:Polynomial Selection: Adding workunit
        c8_235_polyselect_0-100000 to database
        Info:Polynomial Selection: Adding workunit
        c8_235_polyselect_100000-200000 to database
        ...

and now I'm stuck.  What next?

Note that I blew away the entire $(workdir) and any orphan polyselect2l
process between each successive run of cadofactor.py

Thanks for any assistance which may be forthcoming.

Paul (this one)