Fix infinite loop bug in doctest from #36581

[grhkm21]

Discovered by tornaria here.

Sorry for the incorrect implementation! Please merge this quickly, before the next beta (I think).

[grhkm21]

Should "p: CI Fix" be added?

[tscrim]

Please be sure to test this locally:

**********************************************************************
File "src/sage/stats/distributions/discrete_gaussian_lattice.py", line 484, in sage.stats.distributions.discrete_gaussian_lattice.DiscreteGaussianDistributionLatticeSampler.__init__
Failed example:
    v = vector(ZZ, n, (0, 0))
Exception raised:
    Traceback (most recent call last):
      File "/home/travis/sage-build/src/sage/doctest/forker.py", line 715, in _run
        self.compile_and_execute(example, compiler, test.globs)
      File "/home/travis/sage-build/src/sage/doctest/forker.py", line 1147, in compile_and_execute
        exec(compiled, globs)
      File "<doctest sage.stats.distributions.discrete_gaussian_lattice.DiscreteGaussianDistributionLatticeSampler.__init__[23]>", line 1, in <module>
        v = vector(ZZ, n, (Integer(0), Integer(0)))
      File "sage/modules/free_module_element.pyx", line 535, in sage.modules.free_module_element.vector
        raise ValueError("incompatible degrees in vector constructor")
    ValueError: incompatible degrees in vector constructor

It subsequently hangs on line 486.

[tscrim]

See also the linter.

[grhkm21]

My bad. I changed my editor config at some time and must have removed the trailing whitespace highlighting..

[grhkm21]

(I'm fixing the hang(?), give me a second)

[grhkm21]

D.f is not the most descriptive name for a class, so I should refactor it at some point. I will blame it on the original author though 🙈

[tscrim]

Some progress, but now line 501 hangs.

[grhkm21]

It doesn't hang for me..? can you give me a seed

[tscrim]

78175743252608910157834302274104155990

[tscrim]

For the record, I am also testing with --long --verbose

[grhkm21]

I will have a look. I only test with sage -t --verbose without long, but I tested it for 10 times without it looping.. maybe I was lucky

[tscrim]

This one seed seems particularly bad; when I tried a few more times, everything passes.

[grhkm21]

Okay. My _normalisation_factor_zz prints a warning message that it's a bad approximate right? It's really bad. For the vector v in the test case, it outputs 63.x when the true value is 78.x. That determines the computed expected value, so it's way off -> test case loops infinitely. I will just bump up the BOUND and put a TODO...

[grhkm21]

Okay so as it turns out I can't do math. I accidentally coded the solution to $B^N \leq 10^4$ as $B = \log_N(10^4)$. I fixed that and now it works.

[tscrim]

Thank you. Then if the bots come back green, then we can set this to a positive review.

[github-actions]

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