# Newton's method(calculating theta)

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Ahmed Alhawaj on 16 Mar 2020
Answered: Sriram Tadavarty on 16 Mar 2020
w = 30; h = 30; b = 3.5; % In inches
f = @(theta) w*sind(theta) - h*cosd(theta) - b;
fp = @(theta) w*cosd(theta)+h*sind(theta);
theta_newt(1) = 49.76; % Set initial guess
tol=0.4771;
n=1;
while n<=1:50
fe = f(theta_newt(1));
fpe = fp(theta_newt(1));
theta_newt(n+1) = theta_newt(n) - fe(n)/fpe(n);
if theta_newt(n+1)< 49.73-tol || theta_newt(n+1)>49.73+tol
return
else
theta=theta_newt(n+1);
end
n=n+1;
end
disp(theta)
why is the code not returning to the loop when it is not calculating the wanted angle?

Sriram Tadavarty on 16 Mar 2020
Hi Ahmed,
The condition you placed for the while loop is a series of vector. Update the condition as below and code requires minor modifications to work
while n <= 50 % It runs the loop till n becomes 50
fe = f(theta_newt(n));
fpe = fp(theta_newt(n));
theta_newt(n+1) = theta_newt(n) - fe/fpe;
if theta_newt(n+1)< 49.73-tol || theta_newt(n+1)>49.73+tol
return
else
theta=theta_newt(n+1);
end
n=n+1;
end
Hope this helps.
Regards,
Sriram