OpenEuphoria

RE: Uninitialized Variables

• Posted by Chris Bensler <bensler at mail.com> Mar 23, 2002
• 472 views

Derek Parnell wrote:
> ----- Original Message ----- 
> From: "Andy Serpa" <renegade at earthling.net>
> To: "EUforum" <EUforum at topica.com>
> Sent: Sunday, March 24, 2002 10:18 AM
> Subject: RE: Uninitialized Variables
> 
> 
> > > Apparently NAN is (silly me) Not A Number! :P
> > > using equal() compares NAN properly and consistently
> > > 
> > > Here is my revised uninitialized values for variables:
> > > 
> > >    integer  = -INF
> > >    atom     =  INF
> > >    sequence =  NAN
> > >    object   = -NAN
> > > 
> > 
> > So how do I test if something is a nan?  The "official" way is to use 
> > x!=x, but that is usually optimized away by most compilers (& Euphoria, 
> > apparently.)  Using something like if x=1 and x=2 will work in the 
> > interpreter, but not translated to C, even with Watcom.  (In fact, it is 
> > 
> > different depending on the compiler).
> > 
> > Am I stuck with "if x and compare(x/x,1)"?
> > 
> > For my genetic programming system this is a very real problem, as it 
> > comes up with random mathmatical expressions that sometimes are nan's.  
> > If you then take a predicted value (which is a nan) as output for a 
> > function that it has created and compare it with a target value, it will 
> > 
> > show as being equal (& therefore error = 0).  So functions with nan's as 
> > 
> > output get the highest fitness, which is a disaster...
> > 
> 
> This seems to work:
> --------------
> atom x,nan,inf
> inf = 1e300 * 1e300
> nan = inf / inf
> 
> x = nan
> 
> if x = nan then
>     puts(1, "x is not a number\n")
> end if
> ? x = nan
> ? x != nan
> 
> ? nan
> ? inf
> ------------
> 
> 

Derek, try this.

? x=nan
? x=inf
? x=10

btw:   nan = -(inf/inf)


Chris