[Maxima] Maxima parser and global parameters

Richard Fateman fateman at cs.berkeley.edu
Tue Jan 15 18:57:02 CST 2008


I think there is a kind of problem with Ray's proposal. Namely, if someone
writing 0.1r0   (or 1/10) expects that the number would be exactly 1/10.
There is no way in binary floats to do that. 

This is a problem in the perception of the effect, not in implementing
something, though.
I agree with Ray that parsing would be relatively easy; between the two of
us we have written at least 2 such programs recently.:)



> -----Original Message-----
> From: maxima-bounces at math.utexas.edu 
> [mailto:maxima-bounces at math.utexas.edu] On Behalf Of Raymond Toy
> Sent: Tuesday, January 15, 2008 3:06 PM
> To: Stavros Macrakis
> Cc: fateman at EECS.Berkeley.EDU; Maxima at math.utexas.edu; van Nek
> Subject: Re: [Maxima] Maxima parser and global parameters
> 
> Stavros Macrakis wrote:
> > 2) use exact notation instead of floating notation for your 
> numbers, e.g.
> >
> >           block([fpprec:100],
> >               bfloat( sqrt(1000000000000000000001*10^-21) ) );
> >
> > 3) use eval_string or parse_string:
> >
> > I find (2) the most elegant, but perhaps a little clumsy 
> notationally.
> >
> > I wonder if it might be useful to define (e.g.) 1.234x23 ('x' for
> > exact) to mean precisely the rational number 1234*10^(23-3).
> >   
> Some time ago, I suggested (in passing) to use 1.234r23 ("r" for 
> rational).  I think this (either r or x) would be quite easy to 
> implement.  Of course, printing the numbers wouldn't preserve the "r" 
> notation.
> 
> 
> Ray
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