#7719: Improvements to complex AGM
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Reporter: cremona | Owner: AlexGhitza
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-4.3.1
Component: basic arithmetic | Keywords: complex agm
Work_issues: | Author: John Cremona, Robert Bradshaw
Upstream: N/A | Reviewer: Robert Bradshaw, John Cremona
Merged: |
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Changes (by cremona):
* status: needs_work => needs_review
Comment:
This was harder than expected. After applying the two changes suggested
by ylchapuy I found that the code looped on some inputs (e.g. the new
test, which arose from testing period_lattice.py). This led to finding
some other bugs in that cmp_abs function (in cases where a or b is zero
only), and after fixing that I found that the max_exp function returns
something like -2^31 when z=0 which then causes overflow (and the infinite
loop) when the difference d is exactly 0 in the agm code (which does
happen). Hence the extra test for that condition (which seemed simpler
than changing max_exp).
Some minor doctest fixes in the elliptic_curve directory were needed (all
numerical fuzz).
The bugfix patch also contains Robert's original changes (sorry) and then
my actual bugfixes, so only the first and third should be applied.
Anyone else like to review this? Otherwise I'll OK Robert's code (as
adjusted here), but someone needs to check (I did check on 64-bit as well
as 32-bit).
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/7719#comment:13>
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