Add lift_centered for more classes

[lftabera]

This ticket is a split of #8558 for easier review and merging.

Add a lift_centered method to ntl_mod_p elements and a generic function.

If p is an integer mod n, returns r congruent to p mod n such that -n/2 < r <= n/2

It also deprecates the use of centerlift for lift_centered. The discussion is in #8558

Component: basic arithmetic

Keywords: modular arithmetic, centered lift

Author: Luis Felipe Tabera Alonso, Jeroen Demeyer

Branch/Commit: c2255e5

Reviewer: Vincent Delecroix

Issue created by migration from https://trac.sagemath.org/ticket/15804

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

e6bd63b

Deprecate centerlift method

[sagetrac-git]

Changed commit from ddb7291 to e6bd63b

[jdemeyer]

comment:3

I would write the global function lift_centered as

try:
    return p.lift_centered()
except AttributeError:
    return p.lift()

such that it always works on modular objects, even if .lift_centered() has no meaning.

[lftabera]

comment:4

Are you thinking for instance?

K.<x,y,z> = QQ[]
I = Ideal(x*y,x*z,y*z)
R = K.quotient_ring(I)
f = R((x+y+z)**2)
lift_centered(f)
x^2 + y^2 + z^2

So what you propose is that lift_centered should be always a class method and never explicitely computed using the global function, don't you?

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

169cb08

Make global lift_centered function fallback to lift if the object

[sagetrac-git]

Changed commit from e6bd63b to 169cb08

[jdemeyer]

comment:6

In Python, it is better not to use hasattr. Instead, catch AttributeError.

Also, the normal syntax is except AttributeError: (without parentheses).

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

868e571

Catch exceptions instead of using hassattr.

[sagetrac-git]

Changed commit from 169cb08 to 868e571

[lftabera]

comment:8

Fixed, I have also changed the documentation, I hope it is in better shape now.

[sagetrac-git]

Changed commit from 868e571 to 406dca9

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

9da4eab	Merge branch 'master' into u/lftabera/lift_centered
406dca9	Fix import error

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

e81e7a0

Merge branch 'master' into u/lftabera/lift_centered

[sagetrac-git]

Changed commit from 406dca9 to e81e7a0

[jdemeyer]

comment:13

For the newly added docstrings, you should follow the format explained in http://www.sagemath.org/doc/developer/coding_basics.html#documentation-strings. Note that the INPUT and OUTPUT blocks should not be indented and that the docstring shouldn't start with an empty line.

[sagetrac-git]

Changed commit from 3dd232b to 584e874

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

a53a956	Merge tag '6.10.beta6' into u/lftabera/lift_centered
584e874	Trac #15804: Add lift_centered for more classes

[lftabera]

comment:19

Ups, sorry, the docstring format was not good. I have fixed it.

@videlec: After thinking about it, the global namespace is already too big. It should be used for essential functions only. And preferably those that are "classical" or have sense for an arbitrary Sage element. So, I have deleted the global function, the user should depend on the method of each class.

[videlec]

comment:20

Couldn't you do some economy in pari.gen

cdef class gen(gen_auto):
   ...
   lift_centered = centerlift

[jdemeyer]

comment:21

Replying to @videlec:

Couldn't you do some economy in pari.gen

cdef class gen(gen_auto):
   ...
   lift_centered = centerlift

I agree.

[jdemeyer]

Changed branch from u/lftabera/lift_centered to u/jdemeyer/lift_centered

[jdemeyer]

New commits:

c2255e5

For PARI, define lift_centered as alias of centerlift

[jdemeyer]

Changed author from Luis Felipe Tabera Alonso to Luis Felipe Tabera Alonso, Jeroen Demeyer

[jdemeyer]

Changed commit from 584e874 to c2255e5

[videlec]

comment:24

This is good for me.

[jdemeyer]

Reviewer: Vincent Delecroix

[vbraun]

Changed branch from u/jdemeyer/lift_centered to c2255e5