[fixed by #6671] bug in delta_qexp over finite fields

[aghitza]

This is in sage-3.4.2:

sage: delta_qexp(K=GF(5))
TypeError                                 Traceback (most recent call last)
...
TypeError: unable to coerce <type 'sage.libs.ntl.ntl_ZZX.ntl_ZZX'> to an integer

I don't have time to investigate this right now, but it might be a similar issue as #5102.

Component: modular forms

Keywords: delta q-expansion finite field

Issue created by migration from https://trac.sagemath.org/ticket/6020

[craigcitro]

Attachment: trac-6020.patch.gz

[craigcitro]

comment:1

Okay, I've attached a patch. The issue is that we can't coerce from NTL into a finite field.

This patch isn't anything too clever -- I just do the naive thing and work over the base ring from the start instead of using NTL. It runs at the same speed for 100000 terms, and only loses about 3% performance at 1000000, so this should definitely do the job. I'm happy to come back and either unify these (maybe we don't need to manually use NTL anymore?) or do some additional work to speed it up in the finite field case later on.

[williamstein]

comment:2

Wait a minute:
Changing

 if K is ZZ:

to

 if False and K is ZZ:

results in code that is way faster! That's because FLINT kick's NTL's ass, and FLINT is the default for poly's over ZZ now. Just get rid of the flint implementation.

With NTL (on my OS X laptop):

sage: time b = delta_qexp(50000)
CPU times: user 0.44 s, sys: 0.00 s, total: 0.44 s
Wall time: 0.44 s
sage: time b = delta_qexp(100000)
CPU times: user 1.07 s, sys: 0.07 s, total: 1.14 s
Wall time: 1.14 s
sage: time b = delta_qexp(200000)
CPU times: user 2.65 s, sys: 0.06 s, total: 2.71 s
Wall time: 2.72 s

With the "False" as above inserted, so FLINT gets used:

sage: time b = delta_qexp(50000)
CPU times: user 0.21 s, sys: 0.08 s, total: 0.29 s
Wall time: 0.30 s
sage: time b = delta_qexp(100000)
CPU times: user 0.58 s, sys: 0.12 s, total: 0.70 s
Wall time: 0.70 s
sage: time b = delta_qexp(200000)
CPU times: user 1.35 s, sys: 0.33 s, total: 1.68 s
Wall time: 1.68 s