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Add flatter support #40274

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a52088e
Add flatter support
user202729 Jun 20, 2025
dc5a22f
Fix incorrect markup
user202729 Jun 21, 2025
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30 changes: 30 additions & 0 deletions src/sage/features/flatter.py
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Original file line number Diff line number Diff line change
@@ -0,0 +1,30 @@
r"""
Features for testing the presence of ``flatter``
"""

from . import Executable


class flatter(Executable):
"""
A :class:`~sage.features.Feature` describing the presence of ``flatter``.

EXAMPLES::

sage: from sage.features.flatter import flatter
sage: flatter().is_present() # optional - flatter
FeatureTestResult('flatter', True)
"""
def __init__(self):
r"""
TESTS::

sage: from sage.features.flatter import flatter
sage: isinstance(flatter(), flatter)
True
"""
Executable.__init__(self, "flatter", executable="flatter")


def all_features():
return [flatter()]
40 changes: 40 additions & 0 deletions src/sage/matrix/matrix_integer_dense.pyx
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Expand Up @@ -3024,6 +3024,10 @@ cdef class Matrix_integer_dense(Matrix_dense):

- ``'pari'`` -- pari's qflll

- ``'flatter'`` -- external executable ``flatter``, requires manual install (see caveats below).
Note that sufficiently new version of ``pari`` also supports FLATTER algorithm, see
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please provide Pari version info where this appeared. Also, do you know if this already is available from cypari2 ?

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@user202729 user202729 Jun 26, 2025 •
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  • New recursive implementation of the qflll and qflllgram functions
    using the FLATTER reduction algorithm of N. Heninger and K. Ryan.

from https://pari.math.u-bordeaux.fr/archives/pari-announce-24/msg00003.html

so, 2.17.0.

supposedly it's available

sage: pari.version()
(2, 17, 1)

but pari is still slower than flatter on my machine. Demo where LLL is used to compute (integral) kernel of a matrix:

m = random_matrix(ZZ, 25, 50, x=1, y=10^100)
assert m.rank() == 25

%time m.change_ring(QQ).right_kernel_matrix()  # 2.5s
%time m.right_kernel_matrix()  # 8s

%time m1 = (m.T*2^1200).augment(matrix.identity(50)).LLL(algorithm="pari")  # 5s
assert m1[:25,:25]==0

%time m1 = (m.T*2^1200).augment(matrix.identity(50)).LLL(algorithm="flatter")  # 3s (CPU time is small because time is spent in subprocess)
assert m1[:25,:25]==0

more:

%time m.right_kernel_matrix(algorithm='flint')  # 6s
%time m.right_kernel_matrix(algorithm='pari')   # unreasonably long
%time m.right_kernel_matrix(algorithm='padic')  # 8.5s

%time m.change_ring(QQ).right_kernel_matrix(algorithm='flint')  # 2.2s
%time m.change_ring(QQ).right_kernel_matrix(algorithm='padic')  # 2.2s

https://pari.math.u-bordeaux.fr/dochtml/html/Vectors__matrices__linear_algebra_and_sets.html#qflll.

OUTPUT: a matrix over the integers

EXAMPLES::
Expand Down Expand Up @@ -3097,6 +3101,16 @@ cdef class Matrix_integer_dense(Matrix_dense):
[0 0 0]
[0 0 0]

When ``algorithm='flatter'``, some matrices are not supported depends
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the sentence is broken. When is a Germanism, too. You want something like

The ``algorithm='flatter'`` might not support matrices supported by other algorithms.

on ``flatter``. For example::

sage: # needs flatter
sage: m = matrix.zero(3, 2)
sage: m.LLL(algorithm='flatter')
Traceback (most recent call last):
...
ValueError: ...

TESTS::

sage: matrix(ZZ, 0, 0).LLL()
Expand Down Expand Up @@ -3153,6 +3167,17 @@ cdef class Matrix_integer_dense(Matrix_dense):
Although LLL is a deterministic algorithm, the output for
different implementations and CPUs (32-bit vs. 64-bit) may
vary, while still being correct.

Check ``flatter``::

sage: # needs flatter
sage: M = matrix(ZZ, 2, 2, [-1,1,1,1])
sage: L = M.LLL(algorithm="flatter")
sage: abs(M.det()) == abs(L.det())
True
sage: L = M.LLL(algorithm="flatter", delta=0.99)
sage: abs(M.det()) == abs(L.det())
True
"""
if self.ncols() == 0 or self.nrows() == 0:
verbose("Trivial matrix, nothing to do")
Expand All @@ -3177,6 +3202,21 @@ cdef class Matrix_integer_dense(Matrix_dense):
raise TypeError("precision prec must be >= 0")
prec = int(prec)

if algorithm == 'flatter':
import subprocess
cmd = ["flatter"]
if fp is not None or early_red or use_givens or transformation or eta is not None or use_siegel:
raise TypeError("flatter does not support fp, early_red, use_givens, transformation, eta or use_siegel")
if kwds:
raise TypeError("flatter does not support additional keywords")
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would it be more consistent to just ignore kwds here?

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I think it's better practice to complain to the user about invalid data than to silently ignore them.

if delta is not None:
cmd += ["-delta", str(delta)]
stdout = subprocess.run(
cmd, input="[" + "\n".join('[' + ' '.join(str(x) for x in row) + ']' for row in self) + "]",
text=True, encoding="utf-8", stdout=subprocess.PIPE).stdout
return self.new_matrix(entries=[[ZZ(x) for x in row.strip('[] ').split()]
for row in stdout.strip('[] \n').split('\n')])

if algorithm == 'NTL:LLL':
if fp is None:
algorithm = 'NTL:LLL'
Expand Down
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