Beginner's help for a graphic for a free physics textbook

[Christoph Schiller]

With permission form the original author I would like to produce an
improved version of the animated graphic shown at
http://en.wikipedia.org/wiki/File:Snells_law_wavefronts.gif

I'd like to add the animation to my 1600 page physics textbook in pdf  
format
that I offer on the internet for free.
The original graphics was made in MATLAB (the code is given below.)

I have Mac OSX 10.5.6 and downloaded and installed Octave
just to produce this graphic. So I have a few questions (I have never
used either Octave nor MATLAB):

1 - Does the code shown below run on Octave?
2 - How do I input a command file in Octave? (I did not find this in  
the help files)
3 - Will I be able to produce and save the gif on OSX or do I need  
other packages?

(Here is what I plan to change in the graphics of Snell's law:
- introduce a shaded region in blue to show where the water is
- take out the grey line (becomes unnecessary)
- make the blue lines green (to contrast with the blue water)
- make the wave front lines half the thickness they are now (will be  
more pretty)
)

Any help will be appreciated by the readers world-wide - thank you in  
advance!

Best regards

Christoph Schiller
The free physics textbook
www.motionmountain.net


P.S. Here is the original, unmodified code:


% Illustration of Snell's law
function main()

   % indexes of refraction
   n1=1.0;
   n2=1.5;

   sign = -1;% is the source up or down?
   O=[0, -1*sign];
   k=500;


% KSmrq's colors
   red    = [0.867 0.06 0.14];
   blue   = [0, 129, 205]/256;
   green  = [0, 200,  70]/256;
   yellow = [254, 194,   0]/256;
   white = 0.99*[1, 1, 1];
   black = [0, 0, 0];
   gray = 0.5*white;

   color1=red;
   color2=blue;
   color3=gray;
   lw = 3;

   plot_line=0;
   Theta=linspace(0, 2*pi, k);
   V=0*Theta; W=0*Theta;
   S0=7;
   spacing=0.45;
   p=floor(S0/spacing);
   S=linspace(0, S0, p+1);
   spacing=S(2)-S(1);

   num_frames = 10;
   for frame_iter=1:num_frames

      figure(1); clf; hold on; axis equal; axis off;

      % plot the interface between diellectrics
      L=1.2*S0;
      plot([-L, L], [0, 0], 'color', color3, 'linewidth', lw);


      % plot a ray
      plot_line=1;
      s=L;
      theta=pi/3; wfr(s, theta, n1, n2, O, sign, plot_line, color1, lw);

      % plot the wafefronts
      plot_line=0;
      for i=1:p

         s=S(i)+spacing*(frame_iter-1)/num_frames;

         for j=1:k
            theta=Theta(j);
            [V(j), W(j)]=wfr(s, theta, n1, n2, O, sign, plot_line,  
color1,
lw);
         end
         plot(V, W, 'color', color2, 'linewidth', lw);
      end


      %  dummy points to enlarge the bounding box
      plot(0, S0+2.5*spacing, '*', 'color', white);
      plot(0, -(S0+2.5*spacing)/n2, '*', 'color', white);

      % to know where to crop later
      Lx=3.2; Ly=Lx; shift = 1;
      plot([-Lx, Lx, Lx, -Lx -Lx], ...
           [-Ly, -Ly, Ly, Ly, -Ly]+shift);

      file = sprintf('Frame%d.eps', 1000+frame_iter);
      disp(file);
      saveas(gcf, file, 'psc2')
   end

% Converted to gif with the UNIX command
% convert -density 100 -antialias Frame10* Snell_animation.gif
% then cropped in Gimp

function [a, b]=wfr(s, theta, n1, n2, O, sign, plot_line, color1, lw);

   X=O+s*[sin(theta), sign*cos(theta)];

  if( sign*X(2) > 0 )
    t=-sign*O(2)/cos(theta);
    X0=O+t*[sin(theta), sign*cos(theta)];

    if (plot_line == 1)
      plot([O(1), X0(1)], [O(2), X0(2)], 'color', color1, 'linewidth',  
lw,
'linestyle', '--');
    end

    d = norm(O-X0);
    r = (s-d)*(n2/n1)^(sign);

    theta2=asin(n1*sin(theta)/n2);
    XE=X0+r*[sin(theta2), sign*cos(theta2)];
  else
    XE = X;
  end
  a = XE(1);
  b = XE(2);

  if (plot_line==1)
    plot([X0(1), XE(1)], [X0(2), XE(2)], 'color', color1, 'linewidth',  
lw,
'linestyle', '--');
  end