How can use while loop in this case.

I need the code to simulate from my random p (guess value) till it solves the code and gets both f_g and f_l less than the initial guess. I added the while loop so that it runs couple of time additing 0.01 to the guess value till the statement is true. But I fail to understand what went wrong. Please help! I'm new with Matlab.

clc
clear all
%Temperature and pressure
T = 173.15; %K
p = 3e6;; %Pa (guess)
K=1000;
L=1000;
while all(K, L) < p
p = p - 0.01

%Constant for EOS
Tc = 190.564; %Critical Temerpature (K)
Pc = 4.5992e6; %Critical Pressure (Pa)
Vc = 1.3094e-4; %in m^3/mol
R = 8.3145; %Universal gas constant (J/mol.K)
w = 0.01142 %Acentric factor
k = 0.480 + 1.574*w - 0.176*(w^2);
sqrt_alphaT = 1 + k*(1 - sqrt(T./Tc));
alphaT = (sqrt_alphaT)^2;
%Calculate constants of the EOS.
a = 0.42748*(R*R*(Tc^2)/Pc)*alphaT; %m^3.J.K^0.5/mol^2
b = 0.08664*R*Tc/Pc; %m3/mol
%Soave-Redlich-Kwong EOS defined with an anonymous function
P = @(T,V) R*T./(V - b) - a./(V.*(V+b)); %Pa
%The EOS, C, with an anonymous function
%C = @(T,V) (R*T./V)-(R*T./(V - b) - a./(V.*(V+b))); %Pa/K
%volume
v = 1.2*b; %m3/mol
v_ideal= R*T/p; %m3/mol
%Calculated volume V_l and V_g (m3/mol)
V_l = fsolve(@(V) P(T,V) - p,v);
V_g = fsolve(@(V) P(T,V) - p,v_ideal);
%Calculated initial and final compressibilities
z_l = p*V_l/(R*T);
z_g = p*V_g/(R*T);
%Then solving the related equation
ln_phi_l = (1/(R*T))*(integral(@(V) R*T./V - P(T,V), inf, V_l)) - log(z_l) + (z_l-1);
fugacity_l = exp(ln_phi_l);

ln_phi_g = (1/(R*T))*(integral(@(V) R*T./V - P(T,V), inf, V_g)) - log(z_g) + (z_g-1);
fugacity_g = exp(ln_phi_g);
%Calculating fugacity 
fl= fugacity_l*p;
K = abs(fl);
fg= fugacity_g*p; 
L = abs(fg);
%Tolarance
Tolarence = ((fl/fg)-1)*100;
end
Tolarence 

p

[Walter Roberson]

while all(K, L) < p

if the intention is test that all members of K and all members of L are less than p then

while all([K(:);L(:)] < p)

[Syed Muntaha Manzoor]

Basically the intention is to set a random P value which will run in loops till the condition is satisfied that using the coorect p values both f's are less than that p.

[Walter Roberson]

what does

all(K, L)

mean to you? Is "all" the name of a 2d array?

[Syed Muntaha Manzoor]

I was actually trying to put "all" to refer K and L less than p instead of saying individually.

I tried

while all([K(:);L(:)] < p)
end

But not I'm getting my tollarance >1 which is not accepable. How do I limit it in such a way that K,L < p guessed and also my tollarance <1?

Answer 1

[Jan]

As far as I can see, K and L are scalars. Then replace:

while all(K, L) < p

by

while K < p & L < p

[Syed Muntaha Manzoor]

The code keeps on running and doesnt set an output. Only value it shows out if I guess p=1e6

[Jan]

If you start at p=1e6 and reduce p in steps of 0.01, it might take millions of iterations to find matching results.