How to write proper convergence criteria?
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I am writing a code to simulate the similarity solution for flow over a flat plate. I input some guess value for df2deta2 and want the code to run until it satisfies the boundary condition dfdeta=1 and eta_max. Even when the criteria is not met inside the while loop, it will still output a graph. This is my code so far:
clear all;
eta_max=10;
N=101;
Delta_eta=eta_max/(N-1);
for i=1:N
eta(i)=(i-1)*Delta_eta;
end
f=zeros(1,N);
dfdeta=zeros(1,N);
df2deta2g=zeros(1,N);
for i=1:N
df2deta2g(i)=0.2;
end
tol=0.01;
err=2*tol;
while (err>tol)
f(1)=-0.2;
dfdeta(1)=0;
df2deta2g(1)=0.3; %guess value for df2deta2
for i=1:(N-1)
f(i+1)=f(i)+(dfdeta(i)+dfdeta(i+1))*Delta_eta/2;
dfdeta(i+1)=dfdeta(i)+(df2deta2g(i)+df2deta2g(i+1))*Delta_eta/2;
df2deta2g(i+1)=df2deta2g(i)-(2*f(i)*df2deta2g(i)+2*f(i+1)*df2deta2g(i+1))*Delta_eta/2;
end
dfdeta(N)=1;
dfdeta=dfdeta+(df2deta2g+df2deta2g)*Delta_eta/2;
err=(1-max(dfdeta));
df2deta2=df2deta2g;
end
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