%==========================================================================
%
%           Template Code for FDTD Lab (ECE3300, Lab 4).
%
%       This script represents a skeleton code for completing Lab 4.
%   Follow the instructions on the lab handout to fill in the appropriate
%   values for the blank variables indicated below.
%
%==========================================================================
%
%   James Nagel
%   ECE 3300
%   Oct. 8, 2008

clear all;
close all;

%  Physical Constants
e_0 =             %  Permittivity of free space (F/m).
m_0 =             %  Permeability of free space (H/m).

%  Simulation parameters.
K  =                        %  Number of grid points.
N  =                        %  Number of time steps (frames).
dz =                        %  Grid spacing (m)
z  = (0:K-1)*dz;            %  Z-axis (m).
T_fr = 2;                   %  Time steps per frame update.

% Initialize Voltage and Current Arrays
V = zeros(1,K);
I = zeros(1,K);

%  Gaussian parameters for voltage generator.
Vg = 1.0;                   %  Amplitude (V).
t0 = 150;                   %  Time-shift (steps).
sigma = 40;                 %  Standard deviation (steps).

%  Axis scaling.
Vmax = 2;                   %  Voltage y-scale (V).
Imax = 20;                  %  Current y-scale (mA).

%  Transmission line parameters for RG-58.
b   = (2.95/2)*1e-3;            %  Outer conductor radius (m).
a   = (0.812/2)*1e-3;           %  Inner conductor radius (m).
e_r =                           %  Innter dielectric constant. 
L   =                           %  Inductance (H/m).
C   =                           %  Capacitance (F/m).
R   =                           %  Resistance (Ohm/m).
G   =                           %  Conductance (Mho/m).

%  Propagation velocity (m/s)
vp =  

%  Critical time step.
dt = 

% Define update-equation constants.       
c1 = 
c2 = 
c3 = 
c4 = 

%  Initialize figure with two subplots.  The top plot is the voltage and
%  the bottom plot is the current. 
fig = figure(1);
clf
set(fig,'units','pixels','position',[100, 100, 640, 480]);
set(fig,'color',[1 1 1]/1.5);
subplot(2,1,1);
lineV = plot(z,V,'r','linewidth',2);
axis([min(z) max(z) -Vmax Vmax]);
grid on
ylabel('Voltage (V)');
xlabel('Position (m)');
subplot(2,1,2);
lineI = plot(z,[I(1:end-1) I(end-1)]*1e3,'b','linewidth',2);
axis([min(z) max(z) -Imax Imax]);
grid on
ylabel('Current (mA)');
xlabel('Position (m)');

%   FDTD loop
for n = 1:N
    
    %  Set the generator voltage.
    V(1) = Vg*exp(-(n-t0)^2/(2*sigma^2));   %  Gaussian pulse.
    
    %  Voltage update equation loop.   
    for k = 
       
    end
    
    %  Current update equation loop.
    for k = 
        
    end
    
    %  Set the Right-most boundary condition on the current sample.
    I(end) = 

  	%  Only update the plot after a few iterations to make the simulation
  	%  run faster.
    if mod(n,T_fr) == 0
    
        if (any(isnan(V)))
            error('Simulation Terminated Due to Instability.');
        end
        
        %  Remember to convert I to mili-amps.
        set(lineV,'ydata',V);
        set(lineI,'ydata',I*1e3);
        drawnow;
    end

end