Re: How to use existing variable

[Leo Butler]

On Fri, 5 Nov 2010, Neil Ghosh wrote:

< Hi,
< 
< I have a variable X=csvread('XXXX'); with huge data in it.
< 
< My function is written in a .m file  "MyPrg.m" and it uses the data in X and 
have reference to that variable.
< 
< Whenever I call MyPrg in command line it give me error 'X' is undefined , 
however I dont have "clear" in my function
< It should recognize the global variable X.
< 
< I can not afford to read that huge file everytime in my function code.
< 
< Please help
 
 You should look at how to use a global or persistent variable.
 Here is a function that simply memorises the arguments it
 has seen, except when G is empty, when something special 
 is done. You could replace this with your cvsread command.

function y = fng(x)
  global G;
  if isempty(G)
    G=1;      # this only gets executed once
  endif
  y=G=[x,G];  # now do something...
endfunction

Note that until G is declared global outside of the function
scope, G behaves like a persistent variable local to the
function and you will get an error message if you try to
use G outside of the function.

Leo


====
octave> function y = fng(x)
>   global G;
>   if isempty(G)
>     G=1;
>   endif
>   y=G=[x,G];
> endfunction
octave> fng(2)
ans =

   2   1

octave> G
error: `G' undefined near line 65 column 1
octave> fng(3)
ans =

   3   2   1

octave> global G;
octave> G
G =

   3   2   1

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