What is the difference between _coeff_isneg(expr) and expr.could_extract_minus_sign()

[Paul Royik]

Seems like they do the same thing or no?

In printing _coeff_isneg is used, in other packages could_extract_minus_sign.

[Oscar Benjamin]

I'm not sure but I think that could_extract_minus_sign is used for
canonicalisation of the sign in an expression:

In [13]: e1 = -((y - x)*z)

In [14]: e2 = ((x - y)*z)

In [15]: e1
Out[15]: -z⋅(-x + y)

In [16]: e2
Out[16]: z⋅(x - y)

In [17]: e1.could_extract_minus_sign()
Out[17]: True

In [18]: e2.could_extract_minus_sign()
Out[18]: False

The idea is that you can check this method and then (possibly) extract
a minus sign in order to place it into a canonical form. The canonical
form is useful because equivalent expressions will then be equal.

I don't know what the _coeff_isneg function is.

On Mon, 10 Aug 2020 at 19:39, Paul Royik <distan...@gmail.com> wrote:
>
> Seems like they do the same thing or no?
> In printing _coeff_isneg is used, in other packages could_extract_minus_sign.
>

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