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MathGroup Archive 1999

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Re: Real roots and other assumptions...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg19901] Re: Real roots and other assumptions...
  • From: paulh at wolfram.com (P.J. Hinton)
  • Date: Mon, 20 Sep 1999 20:42:25 -0400
  • Organization: "Wolfram Research, Inc."
  • References: <7s3p1u$ck5@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

In article <7s3p1u$ck5 at smc.vnet.net>, Janus Wesenberg <jaw at imf.au.dk> writes:

>I keep encountering problems of the following type when using mathematica:
>I want to solve some equation(s) under some assumptions about the unknown(s),
>e.g. find the real roots of (x-1)(x^2+1).
>I've tried Solve[{Im[x]==0,(x-1)(x^2+1)==0},x]] for the above problem, but that
>doesn't get me anywhere.
>
>Is there a general way to let Mathematica know about such additional bounds as
>non-complexness etc? -- if so I would be happy to know it!

As of Mathematica 4, the only functions which support the ability to specify
conditions on the nature of symbols are Integrate[] and Simplify[].  There
is no mechanism for placing restrictions on the roots returned by solve.
You can feed the result of solve to a post-processing function which 
tests only for real roots, provided that the values of the replacement
rules are numbers.

>PS. I'm using Mathematica from a HP-UX 10 system, and the notebook interface
>have grave difficulties handling large expressions (they scrambled to complete
>nonsense). The local system administrator just says "Use the text access", but
>does anyone know how to make the notebook interface work?

What do you define as "making the interface work"?  Your description of the
problem is too vague for any remedies to be prescribed.  If you are dealing
with large calculations, it is probably better to run without the notebook
interface because it allows you to run the processes in the background as
batch jobs.  In addition, the act of formatting large expressions into 
two-dimensional box forms can require large amounts of resources (time
and memory).  If you do feel that the notebook front end is indispensible,
try setting the default output format type to OutputForm instead of 
StandardForm (Cell -> Default Output Format Type -> OutputForm).  This
keeps the kernel from trying to form box expressions for its results.

--
P.J. Hinton
Mathematica Programming Group           paulh at wolfram.com
Wolfram Research, Inc.
Disclaimer: Opinions expressed herein are those of the author alone.


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