Re: Sign Declaration

*To*: mathgroup at smc.vnet.net*Subject*: [mg80282] Re: Sign Declaration*From*: Bhuvanesh <lalu_bhatt at yahoo.com>*Date*: Thu, 16 Aug 2007 04:52:52 -0400 (EDT)

Specifying the sign of an expression by using Sign[var]^=1 or x/:Sign[x]=1 is not recommended, as these have the potential to interact poorly with built-in functions. A better way is to use the assumptions mechanism: In[1]:= $Assumptions = {Sign[x]==1}; In[2]:= Refine[Sign[x^2]] Out[2]= 1 In[3]:= Simplify[Sign[x^2]] Out[3]= 1 Bhuvanesh, Wolfram Research