Iteration of Ideal Gas Law

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Sohel Rana 2021-3-2

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编辑： Cris LaPierre 2021-5-13

Hi,

How can I do the iteration for the follwoing Ideal Gas Law? I would like to use the Vn and get the Pn value and compare the Ln value to the L. When Ln and L are very close, it will stop the iteration. I would really appreciate your help.

P=101325; 
R=8.314;  
r=20*10^-6;  
L=117*10^-6;  
V=pi*r^2*L;  
T=300;  
n=(P*V)/(R*T); 
% Iteration should start from here
Tn=300+273;  
Pn=(n/V)*R*Tn;
stress=Pn;
E=69.22*10^9;  
S=stress/E;  
dL=S*L;  
Ln=L+dL;
Vn=pi*r^2*Ln;

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Walter Roberson 2021-3-3

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Answer 1

Cris LaPierre 2021-3-3

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编辑：Cris LaPierre 2021-5-13

在 MATLAB Online 中打开

Iterations can be done using either for loops or while loops.

If you want to repeat until a condition is met, a while loop is probably the best option. You just need to set up a conditional statement that evaluates as false until your statement is true. For example

L=1;
Ln=5;
while abs(Ln-L)>0.1
    Ln=Ln-1
end
Ln = 4
Ln = 3
Ln = 2
Ln = 1

There is one thing to be careful of. It is possible to create what is called an infinite loop. This occurs when your contidional statement is always false.

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Cris LaPierre 2021-3-3

编辑：Cris LaPierre 2021-3-3

在 MATLAB Online 中打开

I haven't given you the whole solution. In the code you shared originally, you calculate Ln right before you use it.

Ln=L+dL;
Vn=pi*r^2*Ln;

If you need to use the current value of Ln as L in the next loop, then yes, you should set Ln=L before the loop, and update all uses of L inside the loop to be Ln.

If you don't understand how loops work, I suggest looking at Ch 13 of MATLAB Onramp. It covers for loops, not while loops, but the underlying principles are the same.

Sohel Rana 2021-3-3