Re: creating built-in variables and extracting formulas from anonymous functions

[Geordie McBain]

On Thu, 2007-03-15 at 13:14 -0700, Eric S. Carlson wrote:
> 1. Is there some way to define and initialize a built-in variable
> dynamically at startup? Or is there another type of variable I can use that
> does not get erased with the clear command?

One way is to fake a variable with a function in an m-file.  The file
will still be there to read after a clear.  You can even change the
value of the variable by hiding a persistent variable inside the
function.  Admittedly this does have a different syntax to the usual
variable assignment.

Example.  Say before you start Octave you add
%<---
eulermascheroni1 = 0.577215664901532860606512;
%<---
to the file .octaverc in your working directory and create the file
eulermascheroni2.m:
%<---
function g = eulermascheroni2 (x)
  persistent g0 = 0.577215664901532860606512
  if nargin>0, g0=x; endif
  g = g0;
endfunction
%<---
then in Octave:
%<---
octave:1> eulermascheroni1
eulermascheroni1 =  0.57722
octave:2> eulermascheroni2
ans =  0.57722
octave:3> clear
octave:4> eulermascheroni1
error: `eulermascheroni1' undefined near line 4 column 1
octave:4> eulermascheroni2
ans =  0.57722
octave:5> eulermascheroni2 (0.58)
ans =  0.58000
octave:6> clear
octave:7> eulermascheroni2 (0.58)
ans =  0.58000
octave:8>