MathGroup Archive 2001

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Limit[ Sign[],x->Infinity ]

  • To: mathgroup at
  • Subject: [mg27289] Limit[ Sign[],x->Infinity ]
  • From: Jack Goldberg <jackgold at>
  • Date: Fri, 16 Feb 2001 03:58:51 -0500 (EST)
  • Sender: owner-wri-mathgroup at


I give you two examples using ver. 4.0 on a Mac and a unix system.

	Limit[ Sign[x]*Sign[z],x->Infinity ]  

yields Sign[z]  which is good.

	Limit[ Sign[x]+Sign[z],x->Infinity] 

yields an expression too ugly to present to a wide audience, which is bad. 
Its not a bug since 

	Limit[ Sign[x]+Sign[z],x->Infinity]//FullSimplify

yields 1+Sign[z] which is good.

I propose the name "buglet" to describe such "features" :-).  By the way,
I tried some obvious variations on combinations of Sign[z] and Sign[x] and
found it pretty hard to predict the output. 

Happy hunting



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