Mathematica 9 is now available
Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2009

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: confused about == vs === in this equality

  • To: mathgroup at smc.vnet.net
  • Subject: [mg103760] Re: confused about == vs === in this equality
  • From: David Bailey <dave at removedbailey.co.uk>
  • Date: Mon, 5 Oct 2009 07:38:15 -0400 (EDT)
  • References: <20091003104738.LCJ3I.416659.imail@eastrmwml34> <ha9qqp$7vi$1@smc.vnet.net>

Nasser Abbasi wrote:

> 
> I guess I am a little confused about the "expression" bit in the definition.
> 
> So, when using the 3"=", it is looking at the _value_ of the expression, but 
> when using the 2"=", it is looking at the expression _as it is_, i.e. 
> without evaluating it?  Is this the difference?  I've always used the 2"=" 
> for equality, now I have to be more careful which to use.
> 
> --Nasser 
> 
> 
> __________ Information from ESET NOD32 Antivirus, version of virus signature database 4478 (20091003) __________
> 
> The message was checked by ESET NOD32 Antivirus.
> 
> http://www.eset.com
> 
> 
> 
> 
No - both comparisons evaluate both sides before comparing. The real 
issue is that i==3 will return unevaluated if i does not have a value, 
whereas i===3 will return False unless i has the value 3 . === compares 
things as they are (after evaluation), it never returns unevaluated.

The comparison operator == is a little picky as to what it compares. I 
am not certain, but possibly it does not 'like' comparing one infinity 
with another for mathematical reasons.

David Bailey
http://www.dbaileyconsultancy.co.uk



  • Prev by Date: What Mathematica "says" on two BBP type infinite sums ?
  • Next by Date: Re:Re: Paper heading: does not work?
  • Previous by thread: Re: confused about == vs === in this equality
  • Next by thread: Re: confused about == vs === in this equality