Global variables in function

[Corsair]

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?

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