Variable input argument invalid (function)

if true
function [ theta, E, D,FL] = OP1(AngleMax,necktodiameter,alpha,beta)
global a b
a = 52; %fixed at a rate of 52 degree
b = 15; %fixed at a rate of 15 degree
theta = (AngleMax)-(2*asind(1./(necktodiameter)));
E = cosd(theta/2) - sind(alpha).*cosd(beta).*cosd(a).*cosd(b);
D = ((1-((sind(alpha)).^2*(cosd(beta).^2).^2))*(1-(cosd(a)).^2*(cosd(b).^2))) - E.^2;
FL = acosd((((((-sind(beta)).*(cosd(a)).*(sind(b))) + ((cosd(alpha)).*(cosd(beta)).*(sind(a)))).*E)...
  - ((((cosd(alpha)).*(cosd(beta)).*(cosd(a)).*(sind(b)))+((sind(beta)).*(sind(a)))).*sqrt(D)))....
  /((1-sind(alpha).^2.*cosd(beta).^2).*(1-cosd(a).^2.*cosd(b).^2)));
end

Dear all,

When I try to put the function in command with many variables of beta, the value of FL is only one.

For example:

>> [ theta, E, D, FL] = OP1(180,2,35,[10,15,20])

Others value come with 3 values, but FL only one value

Help me