function	discreteplot( arg, func, req_axis);
% FUNCTION:     discreteplot
%
% SYNOPSIS:     discreteplot( X, Y [, REQAXIS]);
%
% DESCRIPTION:  discreteplot plots the sequence Y 
%               as a function of vector X with 
%               vertical lines from the abscissa to the 
%               function value point. REQAXIS is an axis
%               vector for the user who does not want the
%               defaults (see documentation for axis or enter
%               help axis in the command window to see the 
%               format of the axis vector). Dotted lines
%               linearly interpolate the graph envelope unless
%               there are more than 100 lines.
%
% EXAMPLE:	figure, subplot(2,1,1),
%               t = 0:.05:1;
%               discreteplot(t,sin(t));
%               subplot(2,1,2),
%               t = 0:.05:5;
%               discreteplot(t,sin(t));
%

%
% AUTHOR:	Neil Getz
% DATE:		5-13-92
%
% COPYRIGHT 1992, Neil Getz
%
if (nargin<2 | nargin>3)
   help discreteplot; 
   return;
end

if ( length(arg) ~= length(func)),
   error('Argument lengths must be equal.');
   return;
end

ENVMAX = 100; % largest number of data points for which the envelope is
              % plotted.

% Set coordinates of graph extremes if these have not been specified
% as arguments.
if (nargin==2),
   ylow = 1.1*min([0 min(func) ]);
   yhigh = 1.1*max([0 max(func) ]);
   axis([ min(arg) max(arg) ylow yhigh ]);
elseif (nargin == 3)
   axis( req_axis );
end

% Plot the function envelope if the length of arg is not too long.
if (length(arg) < ENVMAX+1),
   plot(arg,func,'r:');
else % otherwise just plot function value points.
   plot(arg,func,'r.');
end;

% Find out the actual graph extreme coordinates used.
v = axis; % Gets axis values and frees axes.
% Draw a horizontal line at func = 0.
% Draw vertical perpendiculars from the zero line to the data points.
ra = row(arg);
X = [v(1), ra; v(2), ra];
Y = [0, zeros(size(ra)); 0, row(func)];
hold on, plot(X,Y,'-r'); hold off;