function [] = prob_16_1_pt_a()
% 
% Written by:
% -- 
% John L. Weatherwax                2006-09-07
% 
% email: wax@alum.mit.edu
% 
% Please send comments and especially bug reports to the
% above email address.
% 
%-----

close all; 

x_grid = linspace( -3, +3, 25 ); 

indlt = find( x_grid <= 0 ); 
indgt = find( x_grid >  0 ); 

% Draw the x-t diagram solution to this Riemann problem (at time="time"):
% 
time=1.0; 

fpqr = 12; % the characteristic speeds in the right state

x_grid_at_time = zeros(size(x_grid)); 
x_grid_at_time(indlt) = x_grid(indlt);
x_grid_at_time(indgt) = x_grid(indgt) + fpqr*time;

figure; hold on; 
%line( [ x_grid; x_grid_at_time ], [ zeros(size(x_grid)) ; time*ones(size(x_grid)) ] ); 
line( [ x_grid; x_grid_at_time ], [ 0; time ] ); 
%axis( [ -1 2 0 1 ] ); 
xlabel( 'x' ); ylabel( 't' ); %grid on; 
saveas( gcf, 'prob_16_1_pt_a.eps', 'psc2' );