%  Program to plot the hyperbola  
%      y^2/a^2 - x^2/b^2 = 1
%  The hyperbolae are open up/down, so that x is the independent variable
%  for plotting.  (Using the form x^2/a^2 - y^2/b^2 = 1 requires that y be
%  the independent variable, which is awkward programming-wise.)

clear                            % all variables
figure(1), hold off              % start a new figure
set(gca,'FontSize',14)           % adjust fontsize
xmax = 30; ymax = 20;
x = linspace(-xmax,xmax,1001);   % array of x values for plot (why 1001?)
a = 5; b = 3;
y = ???????????;                 % corresponding y values
plot(x,y)
hold on                          % add to current plot
plot(x,-y)                       % Plot other half of hyperbola
axis([-xmax xmax -ymax ymax])    % specify axis limits
xlabel('x')
ylabel('y')
title(['Hyperbola $y^2/a^2 - x^2/b^2 = 1$; $a$ = ', num2str(a), ...
       ', $b$ = ', num2str(b),';  (WR 1/21/08)'],'Interpreter','latex')
% Add axes
plot([0 0],[-ymax ymax],'k')     % y axis (black line - 'k')
plot([-xmax xmax],[0 0],'k')     % x axis