% Animates the propagation of a step source on a lossless transmission line
% with a resistive source and load. The step at the source is 2
% volts high.The source has internal resistance Rg and is attached to the
% line at z=-L.  The load resistance is RL and the load is attached to the
% line at z=0.
% This m-file was written at the University of Wyoming in the Electrical
% and Computer Engineering Department and is to be distributed without
% cost.
clear all
Vg=10;
Z0=50;
Rg=25;
RL=75;
disp(['   The Source Voltage Vg = ' num2str(Vg)]);
disp(['   The Source Resistance Rg = ' num2str(Rg)]);
disp(['   The Characteristic Impedance Z0 = ' num2str(Z0)]);
RL=input('   The Load Resistance RL = '); 
V0=Vg*Z0/(Z0+Rg);
gammaL=(RL-Z0)/(RL+Z0);
gammag=(Rg-Z0)/(Rg+Z0);
a0=V0;a1=gammaL*a0;a2=gammag*a1;a3=gammaL*a2;
if gammaL>=0&gammag>=0;
    lim1=1.2*(a0+a1+a2+a3);
    lim2=-.2*V0;
end
if gammaL<0&gammag<0;
    lim1=1.2*V0;
    lim2=-.2*V0;
end
if gammaL>0&gammag<0;
    lim1=1.2*(1+gammaL)*V0;
    lim2=.2*gammag*gammaL*V0;
end
if gammaL<0&gammag>0;
    lim1=1.2*(a0);
    lim2=-.2*a0;
end
if gammaL==0;
    lim1=1.2*(a0);
    lim2=-.2*a0;
end

z=linspace(-1, 0,201);
w=zeros(1,800);
w(1,301:501)=ones(1,201);
w0=a0*w;
w1=a1*w;
w2=a2*w;
w3=a3*w;
u=w0(1,501:701);

figure(1):clf;
lim=2.2*V0;
axis([-1.1 .1 lim2 lim1]);
plot([0 0],[lim2 lim1]);
hold on;
plot([-1 -1],[lim2 lim1]);
hold on;
plot([-1.1 .1],[0 0]);
hold on;
xlabel('Dimensionless Distance Down the Line, z/L')
hold on;
ylabel('Voltage on the Line, volts')
hold on;
U=[u];
P=plot(z,u,'EraseMode','xor');
VL=[u(1,201)];
V1=[u(1,101)];
T=text(-.9,.9*lim1,'Press Enter to Continue');
pause
set(T,'String','                  ');
%Dc sourcce Vg applied to line at t=0
for i=1:800
    if i>0&i<=199
        u=w0(1,501-i:701-i);  
        set(P,'Ydata',u);
        VL=[VL u(1,201)];
        V1=[V1 u(1,51)];
        pause(.01) 
        if fix(i/2)~=i/2
            U=[U;u];
        end
    end
    
    if i>199&i<=399
        u=w0(1,301:501)+w1(1,-99+i:101+i);
        set(P,'Ydata',u);
        VL=[VL u(1,201)];
        V1=[V1 u(1,51)];
        pause(.01) 
        if fix(i/2)~=i/2
            U=[U;u];
        end
    end
    if i>399&i<=599
        u=w0(1,301:501)+w1(1,301:501)+w2(1,901-i:1101-i);
        set(P,'Ydata',u);
        VL=[VL u(1,201)];
        V1=[V1 u(1,51)];
        pause(.01) 
        if fix(i/2)~=i/2
            U=[U;u];
        end
    end
    if i>599&i<=799
        u=w0(1,301:501)+w1(1,301:501)+w2(1,301:501)+w3(1,-499+i:-299+i);
        set(P,'Ydata',u);
        VL=[VL u(1,201)];
        V1=[V1 u(1,51)];
        pause(.01) 
        if fix(i/2)~=i/2
            U=[U;u];
        end
    end
end
box on
set(T,'String','Press Enter to Continue');
pause
t=linspace(0,4,800);

figure(2);clf
axis([0 t(1,800) lim2 1.1*lim1])
hold on
plot(t,VL,'k--',t,V1,'k-')
xlabel('Dimensionless Time, u_pt/L')
ylabel('Voltage on the Line, volts')
text(2.4,.95*lim1,'- - - denotes v(0,t)')
text(2.4,.9*lim1,'___ denotes v(-0.75L,t)')
text(.5,lim1,'Press Enter to Continue')
box on
pause

figure(3);clf
axis([-1 0 0 3 0 1.5*lim1])
t1=linspace(0,3,81);
z1=linspace(-1,0,51);
UU=[];
for i=0:80
    UU(i+1,:)=U(5*i+1,1:4:201);
end
[Z,T]=meshgrid(z1,t1);
mesh(Z,T,UU,'Edgecolor',[0 0 0]);
newmapdata=colormap;
newmapdata=ones(size(newmapdata));
colormap=newmapdata;
xlabel('Distance, z/L','Rotation',18);
ylabel('Time, u_pt/L','Rotation',-45);
text(-.8,3,lim1,'Press Enter to Continue','Rotation',18)
zlabel('Line Voltage, v(z,t)');
view(330,60)