Counting iterations in a while loop

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Wei-Ta, Huang
Wei-Ta, Huang 2016-5-1
回答： Dhananjay Karad 2022-4-29
How do I now how many iterations do it need to achieve the convergence ?
% Four stroke Otto cycle model
% input parameters
Ti = 300; % inlet temperature, K
Pi = 50; % inlet pressure, kPa
Pe = 100; % exhaust pressure, kPa
r = 10; % compression ratio
qin = 2500; % heat input, kJ/kg (mixture)
gamma = 1.3; % ideal gas specific heat ratio
R = 0.287; % gas constant kJ/kg K
cv= R/(gamma-1); %const vol specific heat, kJ/kg K
f=0.053;% guess value of residual fraction f
Te = 1000; % guess value of exhaust temp, K
tol = 1e-9; % tolerance for convergence
err = 2*tol; %error initialization
gam=(gamma -1)/gamma;
while (err > tol) %while loop for cycle calc
%intake stroke
T1=(1-f)*Ti + f*(1 - (1- Pi/Pe)*gam)*Te;
P1=Pi;
%isentropic compression
P2=P1*r^gamma;
T2=T1*r^(gamma-1);
%const v heat addition
T3=T2 + qin*(1-f)/cv;
P3=P2*(T3/T2);
%isentropic expansion
P4=P3*(1/r)^gamma;
T4=T3*(1/r)^(gamma-1);
%isentropic blowdown
P5=Pe;
T5=T4*(P4/Pe)^(-gam);
%const p exhaust stroke
Te=T5;
fnew=(1/r)*(Pe/P4)^(1/gamma); %new residual fraction
err=abs(fnew-f)/fnew;
f=fnew;
end
%cycle parameters
eta= 1 - 1/r^(gamma-1);
imep = P1*(qin*(1-f)/(R*T1))/(1-(1/r))*eta;
pmep=Pe-Pi;
etanet= eta*(1-pmep/imep);
imepnet= (imep-pmep)/100.;
voleff=1-(Pe/Pi -1)/(gamma*(r-1));
%output calcs
fprintf(' \nFour Stroke Otto Cycle \n')
fprintf('State 1 2 3 4 \n');
fprintf('Pressure (kPa): %6.1f %6.1f %6.1f %6.1f \n',P1,P2,P3,P4);
fprintf('Temperature (K): %6.1f %6.1f %6.1f %6.1f \n',T1,T2,T3,T4);
fprintf('Ideal Thermal Eff.= %6.3f Net Thermal Eff.= %6.3f \n',eta, etanet);
fprintf('Exhaust Temp. (K)= %6.1f Volumetric Eff.= %6.2f \n',Te, voleff);
fprintf('Residual Fraction %6.3f Net Imep (bar)= %6.2f \n',f, imepnet);

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采纳的回答

Geoff Hayes
Geoff Hayes 2016-5-1
To count the number of iterations in your while loop, define a local variable that is incremented for each iteration of the loop. For example,
iterCount = 0;
while (err > tol)
iterCount = iterCount + 1;
% etc.
end
Once outside of the loop, iterCount will tell you how many iterations were performed.
Note that you should always be careful with while loops - you can easily get stuck if your solutions doesn't converge and so your condition is never satisfied. You should always guard against this as
MAX_ITERS = 1000;
iterCount = 0;
while (err > too) && iterCount < MAX_ITERS
iterCount = iterCount + 1;
% etc.
end
In the above, we only allow a maximum of 1000 iterations before exiting the while loop.

更多回答（1 个）

Dhananjay Karad
Dhananjay Karad 2022-4-29
Clear;clc K=0; S=0; While S<12 S=S+K; K=K+1 end Find the iteration in the while loop

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