Why you are worried about creating it in a loop with if condition? You create your phi vector and after just change the sign of phi to get psi.
d2r = pi/180;
g = 30; %upper limit phi
h = -30; %lower limit phi
j = 30; %upper limit theta
l = -30; %lower limit theta
n = 3;
phi = zeros(n,1) ;
theta = zeros(n,1) ;
for k = 1:n
phi(k) = (h + (g-h)*rand(1))*d2r ; %range of limit in phi
theta(k) = (l + (j-l)*rand(1))*d2r ; %range of limit in theta
end
psi = -phi ;
[phi psi]
If you want to go by yout loop method. You need to follow like shown below.
d2r = pi/180;
g = 30; %upper limit phi
h = -30; %lower limit phi
j = 30; %upper limit theta
l = -30; %lower limit theta
n = 3;
for k = 1:n
phi = (h + (g-h)*rand(1))*d2r ;%range of limit in phi
theta = (l + (j-l)*rand(1))*d2r ; %range of limit in theta
if phi > 0
psi = -phi ;
elseif phi < 0
psi = -phi ; % only a chnage here, as phi is already negative, give minus sign or use abs(phi)
end
[phi psi]
end
