Bill Allombert on Wed, 12 Mar 2003 20:46:28 +0100 |
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Re: subst() |
On Wed, Mar 12, 2003 at 02:27:09PM -0500, Walter Neumann wrote: > > subst(p,x^2,x) may be useless, but subst(p,x^2,y) is not. I think Igor was concerned by allowing this when p is not a q(x^2) instead of raising an error. When p(x)=q(x^2) it does make sense, but it make no harm to have substpol for this case. Beside there is a technical issue. PARI 2.1 has {"subst",26,(void*)gsubst,7,"GnG"} where PARI 2.2 has {"subst",99,(void*)gsubst0,7,"GGG"} The new definition cause GP2C to produce less efficient code because it cannot know what the second argument is. > On Wed, 12 Mar 2003, Igor Schein wrote: > > > 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. Cheers, Bill.