Igor Schein on Wed, 12 Mar 2003 14:11:58 -0500

 Re: subst()

```On Wed, Mar 12, 2003 at 06:32:08PM +0100, Karim BELABAS wrote:
> On Tue, 11 Mar 2003, Igor Schein wrote:
> > I remember seeing a recent subst() discussion, which I wasn't paying
> > attention to.  Now I see this behavior, which I don't like at all:
> >
> > ? p=x^2-x-1;
> > ? \y
> >    simplify = 0 (off)
> > ? type(subst(subst(p,x^2,x),x,x^2))
> > "t_INT"
> >
> > I don't see how a transformation from a polynomial to an intereger can
> > be justified, but I'd be glad if someone could make sense out of it.
>
> (18:30) gp > p = x^2 - x - 1;
> (18:30) gp > subst(p,x^2,x)
> %2 = -1
>
> What's wrong with this ? [ x^2 - x - 1 --> (x - x) - 1 = -1 ]

As far as I'm concerned, the above is a correct but also a useless
operations.  I don't see where anyone would use it.  For me an error
would be more useful, detecting that I'm doing something wrong by
mistake.

Do other CAS have anything similar to subst(,x^n,x)?

Igor
```

• Follow-Ups:
• Re: subst()
• From: Walter Neumann <neumann@cpw.math.columbia.edu>
• Re: subst()
• From: Bill Allombert <allomber@math.u-bordeaux.fr>
• References:
• subst()
• From: Igor Schein <igor@txc.com>
• Re: subst()
• From: Karim BELABAS <Karim.Belabas@math.u-psud.fr>