Bill Allombert on Wed, 12 Mar 2003 20:33:44 +0100 |
[Date Prev] [Date Next] [Thread Prev] [Thread Next] [Date Index] [Thread Index]
Re: subst() |
On Wed, Mar 12, 2003 at 02:11:58PM -0500, 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. I suppose Karim has Kronecker trick's in mind: substitute Y by a large polynomial R(X) in P(X,Y) and Q(X,Y), multiply and then replace back R(X) by Y in P... I cannot see another use. Anyway it is not for the faint of heart since it depends on the algorithm used to do the substitution. For example why subst(x^2+1-x^2,x^2+1,y) could not return y-x^2 ? > Do other CAS have anything similar to subst(,x^n,x)? I vote for renaming this subst() 'substpol()' and reinstating the old subst() with the old behaviour. Of course I am biaised since I always disliked overloading. Cheers, Bill.