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Re: "Assuming"

  • To: mathgroup at
  • Subject: [mg85622] Re: "Assuming"
  • From: David Bailey <dave at>
  • Date: Fri, 15 Feb 2008 06:52:58 -0500 (EST)
  • References: <fp0m11$5u7$> <fp192b$gju$> <fp2khg$pka$>

> Compare the following:
> In[8]:= Assuming[x == 0, {x/x^2, x/x, x^2/x}]
> Out[8]= {1/x, 1, x}
> In[9]:= x = 0; {x/x^2, x/x, x^2/x}
> Out[9]= {Indeterminate, Indeterminate, Indeterminate}

Assuming supplies conditions for use by a Simplify (or similar) 
operations within it. It does not initiate a Simplify operation itself. 
Compare for example:

Assuming[x == 1, Simplify[x/x^2]]

Assuming[x == 1, x/x^2]

More generally, I think if Simplify[(a^2-1)(a-1)] returned a conditional 
expression (or did not evaluate at all, as in Simplify[Sqrt[x^2]] ), it 
would be practically useless in more complicated cases - A CAS is meant 
to be a practical tool.

David Bailey

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