Bug in power series expansion

[Tobias Rossmann]

Hi,

the following behaviour of Sage 7.5.1 and 7.6 (Ubuntu 16.04.1, 64-bit) is unexpected:

sage: var('x y0 y1')

(x, y0, y1)

sage: y0.series(x)

1*x + Order(x^20)

sage: y1.series(x)

(y1)

Version 7.4 works fine.

Best,

Tobias

[Ralf Stephan]

Oddly, it always seems to affect the first defined variable apart from x.

Thanks for the bug report.

[TB]

It seems the change in behaviour was introduced in
https://trac.sagemath.org/ticket/21827. In the mean time, one might want
to set the order to positive infinity:

sage: var('x y0 y1')
(x, y0, y1)
sage: y0.series(x)
1*x + Order(x^20)

sage: y0.series(x, +oo)
(y0)

I am not familiar with Pynac internals, so I am not sure what should be
the fix.

Regards,
TB

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[Ralf Stephan]

Fixed in the upcoming beta12, see

https://trac.sagemath.org/ticket/23134