Re: how to create predefined variables

[Paul Kienzle]

Note that you can get around the namespace issue by having a function,
e.g., C, which returns a structure:

function ret = C (varargin)
  static c = Cinit;  # no structure constants so can't populate it 
directly
  if nargin == 0
    ret = c;
  elseif mod(nargin,2)
    usage('C("name",value,...)');
  else
    for i=1:2:nargin,
       if struct_contains(c,varargin{i})
        warning("Replacing definition of constant %s",varargin{i});
       endif
       c.(varargin{i}) = varargin{i+1};
    endfor
  endif
endfunction

function c = Cinit, c.c = 3e8; c.pi=pi; c.R=8.314510; end

You can reference existing constants easily using
        C.c, C.pi, C.R
and add your own using, e.g,
        C('e',e,'i',i,'tol',1e-8)

Anyone want to take ownership of this and add it to octave-forge?

Some outstanding issues:
* An initial list of constants?  (e.g., 
http://physics.nist.gov/cuu/Constants/)
* Do we need to handle a hierarchy of constants?
* How about propagating uncertainties?
* How about propagating units? (e.g., 
http://www.gnu.org/software/units/units.html)
* Can we store and use a description of the constant (e.g., in the help 
text)?

Paul Kienzle
address@hidden

> On Dec 9, 2003 at 6:59am, Paul Kienzle wrote:
>
> pkienz >Date: Tue, 09 Dec 2003 06:59:58 -0500
> pkienz >How about
> pkienz >
> pkienz >function c=R, c=8.314510; end
> pkienz >
> pkienz >Global scope and no need to declare it anywhere.  Of course, I 
> wouldn't
> pkienz >choose the name 'R' unless octave supported namespaces.
> pkienz >
> pkienz >Paul Kienzle
> pkienz >address@hidden
> pkienz >
> pkienz >On Dec 8, 2003, at 8:41 PM, address@hidden wrote:
> pkienz >
> pkienz >> Hmmm... I'd recommend initializing them as global variables 
> in the
> pkienz >> "main" M-file for your Physical Chemistry toolkit:
> pkienz >>
> pkienz >> http://www.octave.org/doc/octave_10.html#SEC67
> pkienz >>
> pkienz >> ~Tomer
> pkienz >>
> pkienz >>
> pkienz >>
> pkienz >> On Dec 8, 2003 at 7:16pm, xuhaida wrote:
> pkienz >>
> pkienz >> xuhaid >Hi:
> pkienz >> xuhaid >   I meet a quetion now. I want to built a physical 
> chemistry
> pkienz >> toolkit by
> pkienz >> xuhaid >Octave, but how
> pkienz >> xuhaid > can I create the constants such as the gas constant
> pkienz >> R(8.314510), the
> pkienz >> xuhaid >speed of the light, etc
> pkienz >> xuhaid >like pi.If not,I have to create these constants for 
> every
> pkienz >> function. Can
> pkienz >> xuhaid >anybody help me?
> pkienz >
> pkienz >



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