Final Edited version

1. I tried running the code, my matlab was having trouble with '.yam1'. When I changed it to '.cti', it ran smoothly. I am not sure why this is happening and if this will affect someone who is trying to use this in matlab.
2. I just added contact info at the end of description file if that's fine.
3. Just curious, if this is the final version, does it show up on the Cantera Matlab examples webpage ?

samples/matlab/Plug_Flow_Reactor.m

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+% General_Plug_Flow_Reactor (PFR) - to solve PFR equations for reactors
+%
+%    This code snippet is to model a constant area and varying area
+%    (converging and diverging) nozzle as Plug Flow Reactor with given
+%    dimensions and an incoming gas. The pressure is not assumed to be
+%    constant here, as opposed to the Python Version of the
+%    Plug Flow Reactor model.
+%
+%    The reactor assumes that the flow follows the Ideal Gas Law.
+%
+%    The governing equations used in this code can be referenced at:
+%    *S.R Turns, An Introduction to Combustion - Concepts and Applications,
+%    McGraw Hill Education, India, 2012, 206-210.*
+%
+%    The current example is written for methane combustion, but can be readily 
+%    adapted for other chemistries.
+%    
+%    Developed by Ashwin Kumar/Dr.Joseph Meadows (mgak@vt.edu/jwm84@vt.edu) on 3-June-2020
+%    Research Assistant/Assistant Professor
+%    Advanced Propulsion and Power Laboratory
+%    Virginia Tech
+
+%% Clear all variables, close all figures, clear the command line:
+clear all
+close all
+clc
+
+% Temperature of gas, in K
+T0 = 1473;
+% Pressure of gas, in Pa
+P0 = 4.47*101325;
+
+% Equivalence Ratio
+Phi = 0.2899;
+
+% Import the gas phase, read out key species indices:
+gas_calc = Solution('gri30.yaml');
+ich4 = speciesIndex(gas_calc,'CH4');
+io2  = speciesIndex(gas_calc,'O2');
+in2  = speciesIndex(gas_calc,'N2');
+nsp = nSpecies(gas_calc);
+x = zeros(nsp,1);
+
+% Change the below values for different Phi values of methane Combustion
+x(ich4,1) = Phi;
+x(io2,1) = 2.0;
+x(in2,1) = 7.52;
+
+% Set the initial state and then equilibrate for a given enthalpy and pressure:
+set(gas_calc,'T',T0,'P',P0,'MoleFractions',x);
+gas_calc = equilibrate(gas_calc,'HP');
+
+%% Calculation of properties along the reactor length
+% The Dimensions and conditions of the reactor are given below
+
+% Inlet Area, in m^2
+A_in = 0.018;
+% Exit Area, in m^2
+A_out = 0.003;
+% Length of the reactor, in m
+L = 1.284*0.0254;
+% The whole reactor is divided into n small reactors
+n = 100;
+% Mass flow rate into the reactor, in kg/s
+mdot_calc = 1.125;
+
+% Flag to indicate whether the area is converging, diverging, or constant:
+% k = -1 makes the solver solve for converging area.
+% k = +1 makes the solver solve for diverging area.
+% k = 0 makes the solver solve for constant cross sectional area
+if A_in>A_out
+    k = -1;
+elseif A_out>A_in
+    k = 1;
+else
+    k = 0;
+end
+
+dAdx = abs(A_in-A_out)/L;
+% The whole length of the reactor is divided into n small lengths
+dx = L/n;
+
+x_calc = 0:dx:L;
+nsp = nSpecies(gas_calc);
+
+% Initialize arrays for T, Y, and rho at each location:
+T_calc = zeros(length(x_calc),1);
+Y_calc = zeros(length(x_calc), nsp);
+rho_calc = zeros(length(x_calc),1);
+
+T_calc(1) = temperature(gas_calc);
+Y_calc(1,:) = massFractions(gas_calc);
+rho_calc(1) = density(gas_calc);
+
+for i = 2:length(x_calc)
+
+    %Solver location indicator
+    fprintf('Solving reactor %d of %d\n', i, length(x_calc))
+
+%--------------------------------------------------------------------------
+%------The values of variables at previous location are given as initial---
+%------values to the current iteration and the limits of the current-------
+%--------------reactor and the gas entering it are being set---------------
+%--------------------------------------------------------------------------
+    inlet_soln(1) = rho_calc(i-1);
+    inlet_soln(2) = T_calc(i-1);
+    inlet_soln(3:nsp+2) = Y_calc(i-1,:);
+    limits = [x_calc(i-1),x_calc(i)];
+    set(gas_calc,'T',T_calc(i-1),'Density',rho_calc(i-1),'MoleFractions',Y_calc(i-1,:));
+    options = odeset('RelTol',1.e-10,'AbsTol',1e-10,'InitialStep',1e-8,'NonNegative',1);
+%--------------------------------------------------------------------------
+%--------------------------------------------------------------------------
+    % These values are passed onto the ode15s solver
+    [~,y] = ode15s(@PFR_solver,limits,inlet_soln,options,gas_calc,mdot_calc,A_in,dAdx,k);
+
+    T_calc(i) = y(end,2);
+    rho_calc(i) = y(end,1);
+    Y_calc(i,:) = y(end,3:nsp+2);
+end
+
+A_calc = A_in+k.*x_calc*dAdx;
+vx_calc = zeros(length(x_calc),1);
+R_calc = zeros(length(x_calc),1);
+M_calc = zeros(length(x_calc),1);
+P_calc = zeros(length(x_calc),1);
+for i=1:length(x_calc)
+    % The gas is set to the solved property values at each location
+    set(gas_calc,'Temperature',T_calc(i),'Density',rho_calc(i),'MassFractions',Y_calc(i,:));
+    % Velocity is calculated from Mass flow rate, Area and Density
+    vx_calc(i) = mdot_calc./(A_calc(i)*rho_calc(i));
+    % Specific Gas Constant
+    R_calc(i) = gasconstant()/meanMolecularWeight(gas_calc);
+    % Mach No. is calculated from local velocity and local speed of sound
+    M_calc(i) = vx_calc(i)/soundspeed(gas_calc);
+    % Pressure is calculated from density, temeprature and gas constant
+    P_calc(i) = rho_calc(i)*R_calc(i)*T_calc(i);
+end
+
+%% Plotting
+plot(x_calc,M_calc)
+xlabel('X-Position (m)')
+ylabel('Mach No')
+title('Mach No. Variation')
+figure(2)
+plot(x_calc,A_calc)
+xlabel('X-Position (m)')
+ylabel('Area (m^2)')
+title('Reactor Profile')
+figure(3)
+plot(x_calc,T_calc)
+xlabel('X-Position (m)')
+ylabel('Temperature')
+title('Temperature Variation')
+figure(4)
+plot(x_calc,rho_calc)
+xlabel('X-Position (m)')
+ylabel('Density (kg/m^3)')
+title('Density Variation')
+figure(5)
+plot(x_calc,P_calc)
+xlabel('X-Position (m)')
+ylabel('Pressure (Pa)')
+title('Pressure Variation')