Re: Global variables in function

[Carlo de Falco]

On 12/nov/08, at 05:42, Corsair wrote:

> Hi all.  I have the follow code:
>
>   global w = 2;
>   global C = 1;
>   global I = 1;
>
>   function vr = r(t)
>     vr = [sin(w * t), cos(w*t), t];
>   endfunction
>
>   function vt = tang(t)
>     vt = [w*cos(w*t), -w * sin(w*t), 1];
>   endfunction
>
>   function db = dB(t, r)
>     db = I * cross(tang(t), f(t) - r) / norm(f(t) - r)^3;
>   endfunction
>
>   dB(1, [1,2,3])
>
> When I run this script, Octave told me that
>
>   error: `w' undefined near line 12 column 9
>   error: evaluating binary operator `*' near line 12, column 10
>   error: evaluating assignment expression near line 12, column 6
>   error: called from `tang'
>   error: evaluating argument list element number 1
>   error: evaluating binary operator `*' near line 16, column 10
>   error: evaluating binary operator `/' near line 16, column 37
>   error: evaluating assignment expression near line 16, column 6
>   error: called from `dB'
>   error: near line 19 of file `test.oct'
>
> Anyone know the problem?


(...)
It is necessary declare a variable as global within a function body
in order to access it.  For example,

    global x
    function f ()
      x = 1;
    endfunction
    f ()

does _not_ set the value of the global variable `x' to 1.  In order to
change the value of the global variable `x', you must also declare it
to be global within the function body, like this

    function f ()
      global x;
      x = 1;
    endfunction
(...)


The explanation above was obtained by typing "doc global" at the  
octave prompt.

c.