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truncate_neg() fails on LaurentSeriesRing(QQ) when valuation is positive #39710

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user202729 opened this issue Mar 15, 2025 · 3 comments · Fixed by #39711
Closed

truncate_neg() fails on LaurentSeriesRing(QQ) when valuation is positive #39710

user202729 opened this issue Mar 15, 2025 · 3 comments · Fixed by #39711

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@user202729
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sage: S.<t> = LaurentSeriesRing(QQ)
sage: (t^-2+t^-1+1+t+t^2).truncate_neg(-1)
t^-1 + 1 + t + t^2
sage: (t^-2+t^-1+1+t+t^2).truncate_neg(1)
t + t^2
sage: (t+t^2).truncate_neg(-1)
---------------------------------------------------------------------------
OverflowError                             Traceback (most recent call last)
Cell In[40], line 1
----> 1 (t+t**Integer(2)).truncate_neg(-Integer(1))

File laurent_series_ring_element.pyx:1085, in sage.rings.laurent_series_ring_element.LaurentSeries.t
runcate_neg()

File power_series_poly.pyx:614, in sage.rings.power_series_poly.PowerSeries_poly.__rshift__()

File polynomial_rational_flint.pyx:827, in sage.rings.polynomial.polynomial_rational_flint.Polynomia
l_rational_flint.__rshift__()

OverflowError: can't convert negative value to unsigned long


sage: (t+t^2).truncate_neg(1)
t + t^2
@user202729 user202729 mentioned this issue Mar 15, 2025
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@tscrim
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tscrim commented Mar 17, 2025

The problem is that truncate_neg is starting from a point less than the valuation (in which case, it should just return the original series).

@5iri
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5iri commented Mar 17, 2025

Hi!

What exactly is left to be done here?

@tscrim
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tscrim commented Mar 17, 2025

The optimization noted in #39711.

vbraun pushed a commit to vbraun/sage that referenced this issue Mar 19, 2025
af7cd2f 
sagemathgh-39711: Allow negative shift for flint rational polynomial
    
Fixes sagemath#39710

Note that the behavior is compatible with the existing behavior of e.g.
`ZZ[]`.

### 📝 Checklist

- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
- [x] I have linked a relevant issue or discussion.
- [x] I have created tests covering the changes.
- [ ] I have updated the documentation and checked the documentation
preview.

### ⌛ Dependencies

<!-- List all open PRs that this PR logically depends on. For example,
-->
<!-- - sagemath#12345: short description why this is a dependency -->
<!-- - sagemath#34567: ... -->
    
URL: sagemath#39711
Reported by: user202729
Reviewer(s): Travis Scrimshaw
vbraun pushed a commit to vbraun/sage that referenced this issue Mar 22, 2025
7a17221 
sagemathgh-39711: Allow negative shift for flint rational polynomial
    
Fixes sagemath#39710

Note that the behavior is compatible with the existing behavior of e.g.
`ZZ[]`.

### 📝 Checklist

- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
- [x] I have linked a relevant issue or discussion.
- [x] I have created tests covering the changes.
- [ ] I have updated the documentation and checked the documentation
preview.

### ⌛ Dependencies

<!-- List all open PRs that this PR logically depends on. For example,
-->
<!-- - sagemath#12345: short description why this is a dependency -->
<!-- - sagemath#34567: ... -->
    
URL: sagemath#39711
Reported by: user202729
Reviewer(s): Travis Scrimshaw
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Allow negative shift for flint rational polynomial user202729/sage
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@tscrim @user202729 @5iri