Your function does not assign a value to the output variable "output".
I suggest you initialize vectors theta and phi inside the funciton, before the for loop. Then populate those vectors, one element at a time, during each loop pass. Then return those vectors from the function to the calling program (such as main.m). Then plot each vector in the calling program. See attached example.
[theta,phi]=RetractionModel2;
figure;
subplot(2,1,1); plot(0:90,theta,'rx-');
title('RetractionModel2');
ylabel('Theta');
subplot(2,1,2); plot(0:90,phi,'rx-');
xlabel('i'); ylabel('Phi');
The modified function is below. Take note of what is different.
function [theta,phi] = RetractionModel2(~)
AB = 0.0732;
AD = 0.0788;
BC = 0.0585;
CD = 0.0575;
a0 = 99.4;
phi=zeros(91,1);
theta=zeros(91,1);
for i= 0:1:90
alpha = a0 - i;
BD = sqrt(AB^2+AD^2-2*AB*AD*cosd(alpha));
delta = asind((AB./BD).*sind(alpha)) ;
beta = 180 - alpha - delta;
psi = acosd((BD.^2+CD^2-BC.^2)/(2*BD*CD));
zeta = asind((CD/BC)*sin(psi));
phi(i+1) = beta - zeta;
theta(i+1) = delta - psi;
end
end
Minor comment: I added semicolons to suppress the display of the intermediate results in the function.
