# to plot alpha(a) vs diameter(D) in the given problem. where A = l*sin(b), B = l*cos(b), C = ( h + 0.5*D )*sin (b) − 0.5*D*tan(b) and E = ( h + 0.5*D)*cos(b) − 0.5*D.

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Rahul Joshi on 15 Sep 2021
Commented: Alan Stevens on 15 Sep 2021
Given equation is A*sin(a)*cos(a) + B*sin(a)*sin(a) − C*cos(a) − E*sin(a) = 0 Also l = 89in., h = 49in. and b= 11.5(angle in degree).
we have to plot alpha(a) vs Diameter(D) using Newton's method where D varies from 30 - 100 inches with a step of 10 inch. plz reply soon.
Rahul Joshi on 15 Sep 2021

Alan Stevens on 15 Sep 2021
Try replacing D within the j-loop by D(j). Also add something like alpha(j) = a after the end of the i-loop (but inside the j-loop). Then you can plot D vs alpha.
I think you will need to increase your value of maxIter to get a converged solution.
You might also think of using a while loop, instead of the i-loop, with an error calculation in order to compare the error to your tola value (which is currently unused).
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Alan Stevens on 15 Sep 2021
%% initial conditions
l = 89;
h = 49;
b1 = 11.5;
D = 30:10:100;
a = 33;
maxIter = 1000;
tola = 1e-6;
err = 1;
%% define function
for j = 1:1:8
A = l*sind(b1);
B = l*cosd(b1);
C = ((h+0.5*D(j))*sind(b1)) - (0.5*D(j)*tand(b1));
E = ((h+0.5*D(j))*cosd(b1)) - (0.5*D(j));
its = 0;
err = 1;
while err>tola && its<maxIter
its = its+1;
aold = a;
f = (A*sind(a)*cosd(a) + B*sind(a)*sind(a) - C*cosd(a) - E*sind(a));
df = (A*cosd(2*a) + B*sind(2*a) + C*sind(a) - E*cosd(a));
a = a - f/df;
err = abs(a - aold);
end
if its==maxIter, disp(j), end
alpha(j) = a;
end
plot(D,alpha),grid
xlabel('D'), ylabel('alpha') R2020a

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