function nnd9nm(cmd,data)
%NND9NM Newton's method demonstration.

% First Version, 8-31-95.

%==================================================================

% BRING UP FIGURE IF IT EXISTS

me = 'nnd9nm';
fig = nnfgflag(me);
if length(get(fig,'children')) == 0, fig = 0; end
if nargin == 0, cmd = ''; end

% CONSTANTS
max_update = 5;
xlim = [-2 2]; dx = 0.2;
ylim = [-2 2]; dy = 0.2;
zlim = [0 12];
xpts = xlim(1):dx:xlim(2);
ypts = ylim(1):dy:ylim(2);
[X,Y] = meshgrid(xpts,ypts);
xtick = [-2 0 2];
ytick = [-2 0 2];
ztick = [0 6 12];
circle_size = 8;

% CREATE FIGURE ========================================================

if fig == 0

  % STANDARD DEMO FIGURE
  fig = nndemof(me,'DESIGN','Newton''s Method','','Chapter 9');
  str = [me '(''down'',get(0,''pointerloc''))'];
  set(fig,'windowbuttondownfcn',str);
  
  % UNLOCK AND GET HANDLES
  
  set(fig,'nextplot','add','pointer','watch')
  H = get(fig,'userdata');
  fig_axis = H(1);
  desc_text = H(2);
  
  % ICON
  
  nndicon(9,458,363,'shadow')
    
  % LEFT AXES
  left = nnsfo('a2','Function F','x(1)','x(2)');
  set(left, ...
    'xlim',xlim,'xtick',xtick, ...
    'ylim',ylim,'ytick',ytick);
  F = (Y-X).^4 + 8*X.*Y - X + Y + 3;
  F = min(max(F,zlim(1)),zlim(2));
  [dummy,func_cont] = contour(xpts,ypts,F,[1.01 2 3 4 6 8 10]);
  cont_color = [nnblack; nnred; nngreen];
  for i=1:length(func_cont)
    set(func_cont(i),'color',cont_color(rem(i,3)+1,:),'linewidth',1);
  end
  text(0,1.7,'< CLICK ON ME >',...
    'horiz','center', ...
    'fontweight','bold',...
    'color',nndkblue);
  
  % RIGHT AXES
  right = nnsfo('a3','Approximation Fa','x(1)','x(2)');
  set(right, ...
    'xlim',xlim,'xtick',xtick, ...
    'ylim',ylim,'ytick',ytick);

  % TEXT
  nnsettxt(desc_text, ...
    'NEWTON''S METHOD',...
    '',...
    'Click anywhere on the graph to create an initial guess. Then the Newton''s method',...
    'trajectory will be shown.',...
    '',...
    'The right graph shows the approximation of function F at the initial point.')

  % CREATE BUTTONS
  drawnow % Let everything else appear before buttons 
  
  set(nnsfo('b4','Contents'), ...
    'callback','nndtoc')
  nnsfo('b5','Close');
  
  % DATA POINTER: MARKER
  marker_ptr = nnsfo('data');
  set(marker_ptr,'userdata',[]);
  
  % DATA POINTER: CURRENT POINT
  point_ptr = nnsfo('data');
  set(point_ptr,'userdata',[]);
  
  % DATA POINTER: PATH
  path_ptr = nnsfo('data');
  set(path_ptr,'userdata',[]);

  % SAVE HANDLES, LOCK FIGURE
  H = [fig_axis desc_text left right marker_ptr point_ptr path_ptr];
  set(fig,'userdata',H)
  
  % LOCK FIGURE AND RETURN
  set(fig,'nextplot','new','pointer','arrow','color',nnltgray)

  nnchkfs;

  return
end

% SERVICE COMMANDS =======================================================

% UNLOCK FIGURE AND GET HANDLES
set(fig,'nextplot','add','pointer','watch')
H = get(fig,'userdata');
desc_text = H(2);
left = H(3);
right = H(4);
marker_ptr = H(5);
point_ptr = H(6);
path_ptr = H(7);

% COMMAND: DOWN

cmd = lower(cmd);
if strcmp(cmd,'down')

  % FIND CLICK POSITION
  axes(left)
  pt = get(left,'currentpoint');
  x = pt(1);
  y = pt(3);
  if (x < xlim(1)) | (x > xlim(2)) | (y < ylim(1)) | (y > ylim(2))
     set(fig,'nextplot','new','pointer','arrow')
     return
  end
  
  % FIND VALUE AT POINT
  Fo = (y-x).^4 + 8*x.*y - x + y + 3;
  if (Fo < zlim(1)) | (Fo > zlim(2))
     set(fig,'nextplot','new','pointer','arrow')
     return
  end
   
  % SHOW POINT
  axes(left);
  delete(get(marker_ptr,'userdata'));
  o_mark1 = plot(x,y,'ok','markersize',circle_size);
  o_mark2 = plot(x,y,'ow','markersize',circle_size+2);
  o_mark3 = plot(x,y,'ok','markersize',circle_size+4);
  set(marker_ptr,'userdata',[o_mark1 o_mark2 o_mark3]);
  
  % REMOVE OLD PATH
  delete(get(right,'children'))
  path = get(path_ptr,'userdata');
  delete(path);
  set(path_ptr,'userdata',[]);

  % STORE POINT & DRAW
  set(point_ptr,'userdata',[x y Fo]);
  cmd = 'draw';
end
  
% COMMAND: DRAW

if strcmp(cmd,'draw')
  
  % GET POINT
  point = get(point_ptr,'userdata');
  if length(point) == 0
     set(fig,'nextplot','new','pointer','arrow')
     return
  end
  x = point(1);
  y = point(2);
  Fo = point(3);
  
  % FIND GRADIENT AT POINT
  gx = -4*(y-x)^3 + 8*y - 1;
  gy = 4*(y-x)^3 + 8*x + 1;
  grad = [gx; gy];

  % CREATE HESSIAN
  temp = 12*(y-x)^2;
  hess = [temp 8-temp;8-temp temp];
  
  % CREATE APPROXIMATION
  dX = X - x;
  dY = Y - y;
  Fa = (hess(1,1)*dX.^2 + (hess(1,2)+hess(2,1))*dX.*dY + hess(2,2)*dY.^2)/2 +...
    grad(1)*dX + grad(2)*dY + Fo;
  
  % PLOT CONTOUR
  axes(right);
  delete(get(right,'children'))
  [dummy,func_cont] = contour(xpts,ypts,Fa,10);
  cont_color = [nnblack; nnred; nngreen];
  for i=1:length(func_cont)
    set(func_cont(i),'color',cont_color(rem(i,3)+1,:),'linewidth',1);
  end
  plot(x,y,'ok','markersize',circle_size);
  plot(x,y,'ow','markersize',circle_size+2);
  plot(x,y,'ok','markersize',circle_size+4);

  % OPTIMIZE
  xx = [x zeros(1,max_update)];
  yy = [y zeros(1,max_update)];
  for i=1:max_update
    gx = -4*(y-x)^3 + 8*y - 1;
    gy = 4*(y-x)^3 + 8*x + 1;
    grad = [gx; gy];
    temp = 12*(y-x)^2;
    hess = [temp 8-temp;8-temp temp];
    dxy = -inv(hess)*grad;
    nx = x+dxy(1);
    ny = y+dxy(2);
    xx(i+1) = nx;
    yy(i+1) = ny;
    x = nx;
    y = ny;
  end

  % REMOVE OLD PATH
  path = get(path_ptr,'userdata');
  delete(path);

  % PLOT PATH
  axes(right)
  plot(xx(1:2),yy(1:2),...
    'color',nnred);
  plot(xx(2),yy(2),'o',...
    'color',nndkblue');
  axes(left)
  path1 = plot(xx,yy,...
    'color',nnred);
  xx(1) = [];
  yy(1) = [];
  path2 = plot(xx,yy,'o',...
    'color',nndkblue');
  set(path_ptr,'userdata',[path1 path2])
  drawnow
end

% LOCK FIGURE
set(fig,'nextplot','new','pointer','arrow')