% Options
  frame_background_gray                = true;

  if frame_background_gray
   graphics_toolkit("qt")         % or graphics_toolkit("fltk")
   frame_background = .94*[1 1 1];
   d = 2;                         % amount to add to text sizes
  else
   graphics_toolkit("gnuplot")    % background will be white regardless of value below
   frame_background = .94*[1 1 1];
   d=0;
  endif

 M  = 16;                    % filter length
 h  = ones(1,M)/M;           % filter impulse response
 L  = 100;                   % output segment length
 La = 500;                   % input data length
%randn("seed","reset")       % experiment with data generator
%seed = randn("seed")        % print value, in case want to use it again
 randn("seed", e)            % generate same data as Overlap-save_algorithm.svg
 a = 1 + randn(1,La)/3;      % data to be filtered
 seg = 2;                    % segment to be computed
 N   = L + M-1;              % DFT size (a power-of-2 would be more efficient)
 Xa  = seg*L + (1:L);        % indices of segment to be filtered

% (https://octave.org/doc/v4.2.1/Graphics-Object-Properties.html#Graphics-Object-Properties)
% Speed things up when using Gnuplot
  set(0, "DefaultAxesFontsize",10+d)
  set(0, "DefaultTextFontsize",12+d)
  set(0, "DefaultAxesYlim",[0 2])
  set(0, "DefaultAxesYtick",[0:2])
  set(0, "DefaultAxesYgrid","on")
  set(0, "DefaultAxesXlim",[0 La])
  set(0, "DefaultAxesXtick",[100:100:La])
  set(0, "DefaultAxesXgrid","on")
  set(0, "DefaultFigureColor",frame_background)
  set(0, "DefaultAxesColor","white")
%=======================================================
  hfig = figure("position",[10 10 912 685], "color",frame_background);

  x1 = .02;               % left margin
  x2 = .02;               % right margin
  y1 = .08;               % bottom margin for annotation
  y2 = .08;               % top margin for title
  dy = .04;               % vertical space between rows

  width = 1-x1-x2;
  height= (1-y1-y2-4*dy)/5; % space allocated for each of 5 rows

  x_origin = x1;
  y_origin = 1;           % start at top of graph area
%=======================================================
  y_origin = y_origin -y2 -height;        % position of top row
  subplot("position",[x_origin y_origin width height])

  plot(1:La, a, "color","blue", Xa, a(Xa), "color","red", "linewidth",2)
  title("One segment of an Overlap-add algorithm", "fontsize",14+d);
  text(1, 2.2, "X[n], with segment k=2 in red", "fontsize",10+d)
%=======================================================
  y_origin = y_origin -dy -height;
  subplot("position",[x_origin y_origin width height])

  plot(1:L, a(Xa), "color","red",...
       L+(1:M-1),zeros(1,M-1), "color","red", "linewidth",2)
  text(250, 1.6, 'X_k[n]')
%=======================================================
  y_origin = y_origin -dy -height;
  subplot("position",[x_origin y_origin width height])

  H = fft(h,N);
  b = real(ifft(H .* fft(a(Xa),N)));    % = conv(h,a(Xa))

  plot(1:N, b, "color","red", "linewidth",2);
  text(250, 1.6, 'Y_k[n], output of FIR lowpass filter');
%=======================================================
  y_origin = y_origin -dy -height;
  subplot("position",[x_origin y_origin width height])

  Xc = 1:seg*L;
  c = conv(h,a(Xc));
  x = (length(c)+1):La;

  plot(1:length(c), c,      "color","blue",...
     x, zeros(1,length(x)), "color","blue", "linewidth",2,...
     seg*L + (1:N), b,  "color","red", "linewidth",2)
  text(250, 1.6, 'Y_2[n-2L]')
%=======================================================
  y_origin = y_origin -dy -height;
  subplot("position",[x_origin y_origin width height])

  Xd = 1:(seg+1)*L;
  d1 = conv(h,a(Xd));
  x = (length(d1)+1):La;

  plot(1:length(d1), d1,    "color","blue",...
     x, zeros(1,length(x)), "color","blue", "linewidth",2)

  xlabel('\leftarrow  n  \rightarrow', "fontsize",12+d)