#7575: mwrank interface improvements
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Reporter: rlm | Owner: cremona
Type: defect | Status: closed
Priority: major | Milestone: sage-4.3.3
Component: elliptic curves | Resolution: fixed
Keywords: | Author: Robert Miller
Upstream: N/A | Reviewer: John Cremona
Merged: sage-4.3.3.alpha0 | Work_issues:
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Comment(by cremona):
I have made some progress in tracking this down.
1. When the mwrank shell starts up, it looks to see if there is a file
in the local directory called PRIMES. If so, it reads in the contents and
uses them (without checking their primality) in a trial division stage of
integer factorization.
2. The function that does that is called initprimes(). This function
is wrapped in Sage but as far as I can see is not called when the library
is used. This should possibly be changed.
3. When integers are factored there is an initial trial division
stage. Primes which are detected this way (e.g. if trial division goes up
to their square root) are added to a list which is maintained for the
session to help in future trial divisions.
4. On exit, if there are any primes in the maintained list (which
might be there either because they are read at the start or added when
found) then that list is output to a file called PRIMES. In the working
directory, and created if it does not already exist, or overwritten if it
does.
Now, two of the curves in the doctests for ell_rational_field.rank, namely
[1,0,0,0,37455] and [0,0,1,-79,342], have large primes in their
discriminants, namely 16180561 and 19047851. These are added to the
maintained list of primes when found, and therefore on exit should be
output to the file PRIMES.
I do not know why the output file is only being produced when mwrank_lib
is used. I would expect it to be the other way round! The writing to
file is done by a function called when a global instance of a C++ class
has its destructor called. I know that that happens when a normal binary
finishes executing (since the compiler puts in calls to relevant
destructors). But I don't see why those destructors would be called when
the library is used. (Until Sage, I had never used my own C++ code as a
library in this way, so my knowledge of C++ runs out here.)
One solution would be to *only* output to the file PRIMES if it already
exists. That way, users of mwrank can still use the functionality it
provides (by creating an empty file at the start) but Sage can ignore it.
This would require a new patch to the eclib code, to be applied after the
one recently applied (p9).
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/7575#comment:24>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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