Having trouble with global array variables

[Olumide]

Hello -

The following script is supposed to use the user-defined cov() function 
to initialize a matrix which is later solved. For some reason, the 
global variable position is either not visible or disappears this 
function. What am I doing wrong?

Thanks,

- Olumide


############################### SCRIPT ###############################

debug_on_warning(1);
debug_on_error(1);

clear height;
clear sigma;
clear position;
clear B;
clear position;

position = [ 0,0,0; 256,0,0; 0,256,0; 256,256,0; 128,128,5 ];
#position = [ 0,0,0; 0,128,0; 256,128,0; 256,0,0; 0,256,0; 256,256,0; 
128,128,5 ];
zeroMatrix = [ 0,0,0; 0,0,0; 0,0,0 ];
zeroVec = [ 0; 0; 0];
dim = size(position)(1);

################### Subroutines ###################

function dist = r( i , x , y )
  global position;
  dist = sqrt( ( x - position(i,1) )^2 + ( y - position(i,2) )^2 );
endfunction


function c = covariance( i, x, y )
  rad = r( i, x, y );
  c = rad^2 * log10(rad);
endfunction


function c = cov( i, j )
  #global position;
  if(i == j)
    c = 0;
  else
    rad = r( j, position(i,1), position(i,2) );
    c = rad^2 * log10(rad);
  endif
endfunction

################### Construct & solve Matrix ###################

for i = 1:dim
  B(i, 1) = 1;
  B(i, 2) = position(i,1);
  B(i, 3) = position(i,2);

  height(i,1) = position(i,3);

  for j = 1:i
    sigma(i,j) = sigma(j,i) = cov(i,j);
  endfor
endfor

M = [[sigma, B];[B',zeroMatrix]];
I = [height;zeroVec];

O = M\I;