Re: Problems with easy simplifications
- To: mathgroup at smc.vnet.net
- Subject: [mg54154] Re: [mg54143] Problems with easy simplifications
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Sat, 12 Feb 2005 01:57:02 -0500 (EST)
- Reply-to: hanlonr at cox.net
- Sender: owner-wri-mathgroup at wolfram.com
Attributes[If]
{HoldRest,Protected}
Clear[H];
H[x_,a_,b_]=If[x<a,a+b,a-b];
Evaluate /@ H[x,1,2]
If[x<1,3,-1]
Clear[H];H[x_,a_,b_]:=If[x<a,Evaluate[a+b],Evaluate[a-b]];
H[x,1,2]
If[x<1,3,-1]
Bob Hanlon
>
> From: Antonio González <gonferh2o at esi.us.es>
To: mathgroup at smc.vnet.net
> Date: 2005/02/11 Fri AM 03:34:47 EST
> To: mathgroup at smc.vnet.net
> Subject: [mg54154] [mg54143] Problems with easy simplifications
>
> I have found some weird behaviors of Mathematica (5.0) related to the
> simplifications of easy expressions.
>
> Take, for instance the function
>
> H[x_, a_, b_] = If[x < a, a + b, a - b]
>
> If I try now to evaluate
>
> H[x,0,0]
>
> the result
>
> If[x < 0, 0 + 0, 0 - 0]
>
> (the values of a and b are irrelevat, a similar result is obtained, for
> instance, with a=1, b= 2, or any integer, real or complex values). I
> cannot force (at least in a simple way) Mathematica to make the addition
> or the substraction. The action of Simplify or FullSimplify leaves the
> expression unchanged while a Map of Simplify
>
> MapAll[Simplify, H[x, 0, 0]]
>
> produces
>
> If[x < 0,
> Simplify[Simplify[0] + Simplify[0]], Simplify[Simplify[
> 0] + Simplify[Simplify[-1] Simplify[0]]]]
>
> Something even worse happens if a use values already defined. For instance
>
> c = 0; d = 0; H[x_] = If[x < c, c + d, c - d]
>
> produces
>
> If[x < 0, c + d, c - d]
>
> In this case, the addition is not necessary.
>
> c = 0; d = 0; H[x_] = If[x < c, c, d]
>
> leads to
>
> If[x < 0, c, d]
>
> Similar problems arise using the function Which.
>
> Any explanation or help with this malfunction would be welcome.
>
> --
>
> Antonio
>
> (Eliminar el agua para responder por e-mail - Remove water to reply by
> e-mail)
>
>