% Options   frame_background_gray = true;    if frame_background_gray    graphics_toolkit("qt")         % has "insert text" option %  graphics_toolkit("fltk")       % has cursor coordinate readout    frame_background = .94*[1 1 1];    d  = 4;                         % 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      xmax = 1000;                    % length of plots   L    = 100;                     % length of rectangles  % (https://octave.org/doc/v4.2.1/Graphics-Object-Properties.html#Graphics-Object-Properties) % Speed things up when using Gnuplot   set(0, "DefaultFigureColor",frame_background)   set(0, "DefaultAxesTitleFontweight","normal")   set(0, "DefaultAxesFontsize",12+d)   % size of numeric tick labels % set(0, "DefaultTextFontsize",12+d)   set(0, "DefaultAxesYlim",[0 2])   set(0, "DefaultAxesXlim",0.02*([-200 xmax]))   set(0, "DefaultAxesYtick",[])   set(0, "DefaultLineLinewidth",2)  %=======================================================   hfig = figure("position",[1 -150 735 835]);    x1 = .02;                     % left margin   x2 = .02;                     % right margin   y1 = .08;                     % bottom margin for annotation   y2 = .10;                     % top margin for title   dy = .10;                     % vertical space between rows    width = 1-x1-x2;   height= (1-y1-y2-3*dy)/4;     % space allocated for each of 4 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])    f = [zeros(1,200) ones(1,L) zeros(1,100)];    plot(0.02*([1:length(f)]-250), f ,"r" )   title("h(t) (non-causal impulse response)", "fontsize",14+d)  %=======================================================   y_origin = y_origin -dy -height;   subplot("position",[x_origin y_origin width height])   plot(0.02*([1:length(f)]-200), f, "b" )   title("h(t-1) (causal impulse response)", "fontsize",14+d)  %=======================================================   y_origin = y_origin -dy -height;   subplot("position",[x_origin y_origin width height])   a = [zeros(1,200) ones(1,L) zeros(1,250) 0.5*ones(1,100) zeros(1,250) 0.25*ones(1,100) zeros(1,200)];   plot(0.02*([1:length(a)]-200), a,"m")   ylim([0 2*max(a)])   title("Input", "fontsize",14+d)  %=======================================================   y_origin = y_origin -dy -height;   subplot("position",[x_origin y_origin width height])   b = conv(a,f);   c = b(200:end);   plot(0.02*([1:length(c)]-250), c, "r", 0.02*([1:length(c)]-200), c, "b")   ylim([0 max(b)])   legend("f(t) non-causal output", "f(t-1) (causal output)")   title("Outputs", "fontsize",14+d)   print -dsvg Illustration_of_causal_and_non-causal_filters.svg