clear all
close all
clc

set(gca,'FontSize',18)
linewidth = 2;

x = -5:0.01:5;
rho = 1/2*(0.9 -0.3*tanh(100*x));
c = 1 - 2*rho;

set(gca,'FontSize',18)
plot(x,rho,'Linewidth',linewidth)
xlabel('x')
ylabel('\rho')
axis([-5,5,0,1])
print -djpeg expansion_fan_rho


figure
set(gca,'FontSize',18)
plot(x,c,'Linewidth',linewidth)
xlabel('x')
ylabel('c')
axis([-5,5,-1,1])
print -djpeg expansion_fan_c

% first draw the characteristics

figure

x_0 = [-5:-1,-0.1];x_0 = [x_0,-x_0];
rho_0 = 1/2*(0.9-0.3*tanh(10*x_0));
c_0 = 1 - 2*rho_0;
t = 0:0.01:5;

for j = 1:length(x_0)
    set(gca,'FontSize',18)
    plot(x_0(j) + c_0(j)*t,t,'b','Linewidth',linewidth)
    axis([-5,5,0,5])
    hold on
end

x_0 = [0.05,0.02,0.01];x_0 = [x_0,-x_0];
rho_0 = 1/2*(0.9-0.3*tanh(10*x_0));
c_0 = 1 - 2*rho_0;
t = 0:0.01:5;

for j = 1:length(x_0)
    set(gca,'FontSize',18)
    plot(x_0(j) + c_0(j)*t,t,'r','Linewidth',linewidth)
    axis([-5,5,0,5])
    hold on
end

hold off
xlabel('x')
ylabel('t')
print -djpeg expansion_fan_characteristics

x = -10:0.01:10;
rho = 1/2*(0.9-0.3*tanh(100*x));
c = 1 - 2*rho;

t_range=0:0.2:5;
delete expansion_fan.gif    %have to delete old one so new one shows up
for j=1:length(t_range)
    set(gca,'FontSize',18)
    t=t_range(j);
    plot(x + c*t,rho,'LineWidth',linewidth)
    axis([-10,10,0,1.1])
    grid on
    title(['t=',num2str(t_range(j) - 0.01,'%1.1f')])
    ylabel('\rho(x,t)')
    xlabel('x')
    pause(0.1)
    gif_add_frame(gcf,'expansion_fan.gif',1);
end