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

[git]

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

​e6bd63b

Deprecate centerlift method

[jdemeyer]

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]

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?

[git]

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

​169cb08

Make global lift_centered function fallback to lift if the object

[jdemeyer]

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

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

[git]

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

​868e571

Catch exceptions instead of using hassattr.

[lftabera]

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

[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

[git]

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

​e81e7a0

Merge branch 'master' into u/lftabera/lift_centered

[jdemeyer]

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.

[git]

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

​2f30718	Merge tag '6.5' into u/lftabera/lift_centered
​fff5565	Merge tag '6.6' into u/lftabera/lift_centered
​7a5e891	Merge tag '6.7' into u/lftabera/lift_centered
​3dd232b	Ticket 15804

[vdelecroix]

What is the purpose of introducing the (globally available) function lift_centered?

[jdemeyer]

13 has not been addressed.

Also, for PARI, you should not deprecate centerlift() since that's the PARI name of the method. You may allow both lift_centered() and centerlift() but do not deprecate centerlift().

[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]

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

@vdelecroix: 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.

[vdelecroix]

Couldn't you do some economy in pari.gen

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

[jdemeyer]

Replying to vdelecroix:

Couldn't you do some economy in pari.gen

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

I agree.

[jdemeyer]

New commits:

​c2255e5

For PARI, define lift_centered as alias of centerlift

[vdelecroix]

This is good for me.