how to take the exact coordinates of non zero values of a matrix

I'm trying to take the non zero values of gaussian spots that i generate random. I round my table but I don't take the exact coordinates I think. Could anybody help me with this? Here is my code in which I save the nonzero coordinates.

    function[n_min,n_max,max_val,spot,x1,y1,n_z]=generate_spot_7(i,sigma_x,sigma_y,x0,y0,n,min_n,max_n)
    new_min=min_n/255;
  new_max=max_n/255;
   n_min=new_min+(new_max-new_min).*rand;
   n_max=(n_min)+(new_max-n_min).*rand;

   Z=0;
   t=0;
   theta=0+i*pi/500;;%allazoume tixaia tis esties ton elipseon

    a = cos(theta)^2/2/sigma_x^2 + sin(theta)^2/2/sigma_y^2;
  %b=0;
  b = -sin(2*theta)/4/sigma_x^2 + sin(2*theta)/4/sigma_y^2 ;
  c = sin(theta)^2/2/sigma_x^2 + cos(theta)^2/2/sigma_y^2;
  %%%c=1;
  [X, Y] = meshgrid(-(n+2*4):.13:(n+2*4), -(n+2*4):.13:(n+2*4));
  t=exp( - (a*(X-x0).^2 + 2*b*(X-x0).*(Y-y0) + c*(Y-y0).^2));
  MAX=max(t);
  o=round(t*100000)/100000;%epeidi einai double kano strogilopoiisi g na paro 
  n_z=find(o~=(0));
  [x1,y1] = ind2sub(size(o),find(o~=0))
  s=[n,n];
  %[x1,y1] = ind2sub(s,n_z)
  max_val=max(MAX);
  spot=t;

I observe that when I add the generated spots and i'm going to zero the values of some spots, I zero more pixels than those I want to zero.

Answer 1

[Sean de Wolski]

n_z = find(~o);
[x1,y1] = ind2sub(size(o),n_z)

[Matt Fig]

Or simply

[x1,y1] = find(~o);

[Mary Kodogianni]

This doesn't seem to work with my images very well.I make images with lots of spots but when I just go to zero the value with coordinates of a particular spot it zeros all of the spots.

I tryed this code instead and It seems to work better but not perfect

[x1,y1] = ind2sub(size(o),find(o));