Sagemath 9.2 Product function Bug

bug
product

asked 2021-02-17 02:00:44 +0200

updated 2021-02-17 02:10:17 +0200

In sagemath 9.2 the product function have a bug in multiplication.

var('q')
var('jt')
((q^(2/3)+q**(2/5))*(product(1 -q**jt, jt, 1 , 31) * q**(1 /24 ))).expand()

returned a result with leading series to be (Both wrong in the powers and the coefficients )

...+ 2*q^(121/24) - 2*q^(49/24) - 2*q^(25/24) + 2*q^(1/24)

while

((q^(2/3)+q**(2/5))*(product(1 -q**jt, jt, 1 , 31) * q**(1 /24 )).expand()).expand()

returned a result with leading series to be

...+ q^(653/120) - q^(65/24) - q^(293/120) - q^(41/24) - q^(173/120) + q^(17/24) + q^(53/120)

Notice that both

((q^(2/3)+q**(2/5))*(product(1 -q**jt, jt, 1 , 30) * q**(1 /24 ))).expand()
((q^(2/3)+q**(2/5))*(product(1 -q**jt, jt, 1 , 30) * q**(1 /24 )).expand()).expand()

returned a result with leading series to be

...+ q^(653/120) - q^(65/24) - q^(293/120) - q^(41/24) - q^(173/120) + q^(17/24) + q^(53/120)

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Comments

Note that :

sage: foo=((q^(2/3)+q**(2/5))*(product(1 -q**jt, jt, 1 , 31) * q**(1 /24 ))).expand()
sage: bar=((q^(2/3)+q**(2/5))*(prod([1-q^u for u in (1..31)]) * q**(1 /24 ))).expand()
sage: bool(foo==bar)
True

In other words, the use of the Python prod on the explicit extension of your factors gives the same result as the (evaluated) symbolic product. The problem may be somewhere else.

Emmanuel Charpentier ( 2021-02-17 10:32:40 +0200 )edit

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sage: var("q, jt") (q, jt) sage: A=q^(2/3)+q**(2/5) sage: B=product(1 -q**jt, jt, 1 , 31)*q**(1 /24 ) sage: bool((A*B).expand()==(A*B.expand()).expand()) False sage: (((A*B).expand())/(A*B.expand()).expand()).factor() 2*q^(1/24)/(q^(17/24) + q^(53/120))

Comments

this is an oldish bug, same happens with almost 3 years old https://github.com/pynac/pynac/releas...

Dima ( 2021-02-17 13:36:15 +0200 )edit

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