Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2005
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2005

[Date Index] [Thread Index] [Author Index]

Search the Archive

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)
> 
> 


  • Prev by Date: Re: Algebraic Symbol Manipulation
  • Next by Date: Re: Problems with easy simplifications
  • Previous by thread: Re: Problems with easy simplifications
  • Next by thread: Re: Problems with easy simplifications