# How to get this help file to run

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Quincey Jones on 20 Feb 2020
Answered: Pravin Jagtap on 26 Feb 2020
function [v,err,count] = MS1_Ideal_Gas(P)
% MS1_Ideal_Gas
% R = 0.082057; % Ideal gas constant in L atm / K mol
% T = 293; % Temperature in K
% P = [1 1.5 2 2.5 3 5 10 15 25 50 100];
% v = zeros(1,length(P));
% for i=1:length(P)
% [u,err,count] = MS1_Ideal_Gas(P(i));
% v(i)=u;
% end
% P1=[1:0.1:100];
% V1=R*T./P1;
% plot(P1,V1) %ideal
% hold on
% plot(P,v,'xr') %Redlich
% title('Molar Volume vs Pressure for Cl_2')
% xlabel('Pressure P (atm)')
% ylabel('Molar Volume v (L/mol)')
% legend({'Ideal Gas Law','Redlich-Kwong Equation'},'Location','northeast')
% Version 1: created 18/02/20. Author: Savana Stewart
% UCD ID: 19208141
% Inputs:
R = 0.082057; % Ideal gas constant in L atm / K mol
T = 293; % Temperature in K
Tc = 416.90; % Critical temperature of Cl_2 in K
Pc = 78.72918; % Critical Pressure of Cl_2 in atm
a = ((R^2)*(Tc^(5/2)))/(9*Pc*(2^(1/3)-1));
b = (R*Tc*(2^(1/3)-1))/(3*Pc);
% P Pressure in atm
% Outputs:
% v equals molar volume (V/n) in L/mol
% err equals modulus of function evaluated at approximate root.
% count is number of iterations taken by Newton-Raphson algorithm.
if (~isscalar(P)) || (~isreal(P)) || P <= 0
error('Input argument P must be positive real scalar.')
end
Iteration_limit = 20; % maximum number of iterations permitted
Tolerance = 10^7; % maximum acceptable value for modulus of
% function evaluated at estimated root3of
A = (a*P)/((R^2)*(T^(5/2)));
B = (b*P)/(R*T);
v = R * T / P; % Molar volume
Z = 1;
C = A-B-B^2; % Substitution to simplify equation
poly_f = [1 -1 C -A*B]; % = (Z^3) - (Z^2) + (A-B-(B^2))*Z - (A*B)
f = polyval(poly_f,Z);
poly_df = [0 3 -2 C]; % = 3*Z^2 - 2*Z + (A - B - (B^2))
for count = 1:Iteration_limit + 1
% Terminate with error message if iteration limit exceeded:
if count == Iteration_limit + 1
error('Iteration limit reached. Iteration did not converge.')
end
df = polyval(poly_df,Z);
Z = Z - (f/df); % Newton-Raphson iteration
% Terminate iteration if function is sufficiently small at current
% estimate
if abs(f) < Tolerance
break
end
end
v = Z*R*T/P; % Subsitiution to find v
% to find numerical values for table 2 in report:
%v1 = R * T / P;
%fprintf('P = %d \nv (Ideal Gas Law) = %d \nv (Redlich-Kwong) = %d \nrequires %d iterations \n \n',P,v1,v,count);
err = abs(f); % Error is magnitude of f(v) at final root estimate
help MS1_Ideal_Gas; % help function
end
When I type in the comments at the beginning if the file into the command window, it runs fine. However, When I tried to turn it into a help file the code no longer runs. How can I change the help file so it acts like I am just typing all of the first comments into the command window?

Pravin Jagtap on 26 Feb 2020
Hello Savana,
The issue which you are facing is not clear from your question and code. I found a similar question you posted as an extension of this question.
I am assuming you are facing issues with the 'help' function and executing the 'MS1_Ideal_Gas' function file. You need to pass the argument 'P' which is scalar value as per code (Make sure that you are in the same directory before executing following command).
>> MS1_Ideal_Gas(1)
Refer to the following link for understanding the usage of 'help' function: