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Hi, my while loop stops before meeting its designated conditions and gives me a result. Why is this?

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Abdul Akif Jabir
Abdul Akif Jabir 2018-11-30
关闭： MATLAB Answer Bot 2021-8-20
while error(end) <= 0.01
[t,z] = ivpSolver_Assignment_2(t0,z0,dt,tend,theta(n));
w(n) = z(1,end);
error(n) = w(n) - 2.1;
theta(n+1) = (-error(n-1)/((error(n)-error(n-1))/(theta(n)-theta(n-1)))) + theta(n-1);
n = n+1;
end
t and z are vectors

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回答（2 个）

Georgios Pyrgiotakis
编辑：Georgios Pyrgiotakis 2018-11-30
If you have not defined error (i.e. error=ones(1,x) where x is the length of the matrice) the loop will stop imedaitely since W(end) by default is null or zero. instead write:
error=[1];
while error(end) <= 0.01
[t,z] = ivpSolver_Assignment_2(t0,z0,dt,tend,theta(n));
w = z(1,end);
error=[error, w - 2.1;]
theta(n+1) = (-error(n-1)/((error(n)-error(n-1))/(theta(n)-theta(n-1)))) + theta(n-1);
end
If you want to also keep the values for w as well, you need to also define w and append values to it.
Georgios Pyrgiotakis
This is correct in the general context, but since your while depends on it the error null value will terminate the loop before even starts. You need to initiate them with values that will work for the calculations later.
theta = [x]; % You need to find a value that can be used for the next theta calculation
w= [];
error=[1];
while error(end) <= 0.01
[t,z] = ivpSolver_Assignment_2(t0,z0,dt,tend,theta(n));
w=[w,z(1,end)];
error=[error, w(end) - 2.1];
theta_tmp = (-error(end-1)/((error(end)-error(end-1))/(theta(end)-theta(end-1)))) + theta(end-1);
theta=[theta, theta_tmp]
end
That should work.

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