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sage.arith.misc: fixes error in binomial for p-adic numbers with negative valuation #35823

Merged
merged 10 commits into from
Dec 26, 2023
29 changes: 28 additions & 1 deletion src/sage/arith/misc.py
Original file line number Diff line number Diff line change
Expand Up @@ -3696,6 +3696,12 @@ def binomial(x, m, **kwds):
0
sage: binomial(RealField()('2.5'), 2) # needs sage.rings.real_mpfr
1.87500000000000
sage: binomial(Zp(5)(99),50)
3 + 4*5^3 + 2*5^4 + 4*5^5 + 4*5^6 + 4*5^7 + 4*5^8 + 5^9 + 2*5^10 + 3*5^11 +
4*5^12 + 4*5^13 + 2*5^14 + 3*5^15 + 3*5^16 + 4*5^17 + 4*5^18 + 2*5^19 + O(5^20)
sage: binomial(Qp(3)(2/3),2)
2*3^-2 + 2*3^-1 + 2 + 2*3 + 2*3^2 + 2*3^3 + 2*3^4 + 2*3^5 + 2*3^6 + 2*3^7 +
2*3^8 + 2*3^9 + 2*3^10 + 2*3^11 + 2*3^12 + 2*3^13 + 2*3^14 + 2*3^15 + 2*3^16 + 2*3^17 + O(3^18)
sage: n = var('n'); binomial(n, 2) # needs sage.symbolic
1/2*(n - 1)*n
sage: n = var('n'); binomial(n, n) # needs sage.symbolic
Expand Down Expand Up @@ -3792,6 +3798,27 @@ def binomial(x, m, **kwds):
sage: binomial(n,2) # needs sage.symbolic
1/2*(n - 1)*n

Test p-adic numbers::

sage: binomial(Qp(3)(-1/2),4) # p-adic number with valuation >= 0
1 + 3 + 2*3^2 + 3^3 + 2*3^4 + 3^6 + 3^7 + 3^8 + 3^11 + 2*3^14 + 2*3^16 + 2*3^17 + 2*3^19 + O(3^20)

Check that :trac:`35811` is fixed::

sage: binomial(Qp(3)(1/3),4) # p-adic number with negative valuation
2*3^-5 + 2*3^-4 + 3^-3 + 2*3^-2 + 2*3^-1 + 2 + 2*3 + 2*3^2 + 2*3^3 + 2*3^4 + 2*3^5 +
2*3^6 + 2*3^7 + 2*3^8 + 2*3^9 + 2*3^10 + 2*3^11 + 2*3^12 + 2*3^13 + 2*3^14 + O(3^15)

sage: binomial(Qp(3)(1/3),10).parent()
3-adic Field with capped relative precision 20

sage: F.<w>=Qq(9); binomial(w,4) # p-adic extension field
(w + 2)*3^-1 + (w + 1) + (2*w + 1)*3 + 2*w*3^2 + (2*w + 2)*3^3 + 2*w*3^4 + (2*w + 2)*3^5 +
2*w*3^6 + (2*w + 2)*3^7 + 2*w*3^8 + (2*w + 2)*3^9 + 2*w*3^10 + (2*w + 2)*3^11 + 2*w*3^12 +
(2*w + 2)*3^13 + 2*w*3^14 + (2*w + 2)*3^15 + 2*w*3^16 + (2*w + 2)*3^17 + 2*w*3^18 + O(3^19)
sage: F.<w>=Qq(9); binomial(w,10).parent()
3-adic Unramified Extension Field in w defined by x^2 + 2*x + 2

Invalid inputs::

sage: x = polygen(ZZ)
Expand Down Expand Up @@ -3872,7 +3899,7 @@ def binomial(x, m, **kwds):
# case 2: conversion to integers
try:
x = ZZ(x)
except TypeError:
except (TypeError, ValueError):
pass
else:
# Check invertibility of factorial(m) in P
Expand Down