Re: [PyGiNaC-users] strange behavior with the test suite

[Jonathan B. <jbr...@ea...>]

On Mon, 2005-10-03 at 20:27 +0300, Matti Peltom=E4ki wrote:
> Hi,
>=20
> while playing around with pyginac, I found some strange behavior with
> the regression test suite. The reason to this behavior escapes me.=20
>=20
> When running ./run python2.3 bin/checkall.py most of the time=20
> everything goes ok, but every now and then an error occurs as follows.
>=20
> *****************************************************************
> Failure in example: exam_normal2()
> from line #1 of exam_normalization.exam_normal2
> Expected: 0
> Got:
> normal form of  (-y+x)**(-3)*(x**2-y**2)  returned  (y-x)**(-2)*(y+x)  wh=
ile=20
> it should be  (-y+x)**(-2)*(y+x)
> normal form of  (x**2-y**2)*(-1/2*y+1/2*x)**(-3)  returned =20
> (y-x)**(-2)*(8*y+8*x)  while it should be  (-y+x)**(-2)*(8*y+8*x)

I think that this is a canonicalization issue.  If hash(x) is greater
than hash(y) (when reinterpret_cast'ed back to unsigned ints), then
pow(x - y, 2) normalizes to pow(y - x, 2)

I'm not sure if this behavior is deliberate so I'm bringing it up on
ginac-list.  In the meantime, a patch has been committed to CVS that
works around the error.

-Jonathan