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Problems with easy simplifications
*To*: mathgroup at smc.vnet.net
*Subject*: [mg54143] Problems with easy simplifications
*From*: Antonio González <gonferh2o at esi.us.es>
*Date*: Fri, 11 Feb 2005 03:34:47 -0500 (EST)
*Sender*: owner-wri-mathgroup at wolfram.com
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)
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