Re: Positive[a] = True ???
- Subject: [mg2618] Re: [mg2518] Positive[a] = True ???
- From: johan at kajsa.isy.liu.se (Johan Gunnarsson)
- Date: Thu, 30 Nov 1995 20:58:27 -0500
- Approved: firstname.lastname@example.org
- Distribution: local
- Newsgroups: wri.mathgroup
- Organization: Wolfram Research, Inc.
If the symbol a is positive then why cannot Mathematica simplify
Sqrt[a^2] to a?
Out= Sqrt[a ]
In article <48ejb3$fi5 at ralph.vnet.net> Allan Hayes <hay at haystack.demon.co.uk> writes:
> Frank Domokos <domokos at chaph.usc.edu>
> in [mg2518] Positive[a] = True ???
> asks about the following kind of response
> IN>> Positive[a] = True;
> OUT>> Set::write: Tag Positive in Positive[a] is Protected.
> Most system functions, like Positive, are protected (have the
> attribute Protected) to avoid unintentional changes. You cannot make
> a definition for them ("tagged" by them) without unprotecting them
> (see later).
> Here are some ways round this for your example
> 1.Tag your definition with a instead of f:
> a. by using UpSet (^=) instead of Set (=):
> Positive[a]^= True;
> or, more specifically,
> b. by using TagSet:
> a/:Positive[a] = True;
> 2. Unprotect Positive to allow definitions to be tagged by it:
> Positive[a] = True;
> (eventually re-protecting Positive)
> Of course if a is protected or is an expression with a protected
> head then you will need to unprotect either Positive or a or the
> head of a.
> Allan Hayes
> hay at haystack.demon.co.uk
| Division of Automatic Control
/|\ Dept. of EE, Linkoping University
\|/ S-581 83 Linkoping, Sweden
/|\ Tel: +46 13 282913
/ | \ Fax: +46 13 282622
() | () Email: johan at isy.liu.se
Prev by Date:
Peculiar behavior of Integrate
Next by Date:
Re: Bug in symbolic inversion of matrices
Previous by thread:
RE: Positive[a] = True ???
Next by thread:
[Q] how fast is each machine with Mathematica ?