The problem is how you're specifying the linetype and when you're doing the plotting. Since you're plotting each point one at a time, there are 361 individual plot objects consisting of no line (because each is only one point) and no marker type.
You can specify a marker type and get a pseudoline
ncont=3.24;
kcont=4.28;
step=pi/180;
limit=2*pi;
for gamma = 0:step:limit
num1=(((ncont*cos(gamma))-1)^2)+((kcont^2)*cos(gamma)^2);
num2=((ncont-cos(gamma))^2)+kcont^2;
den1=(((ncont*cos(gamma))-1)^2)+((kcont^2)*cos(gamma)^2);
den2=((ncont+cos(gamma))^2)+kcont^2;
abs=1-(0.5*((num1/den1)+(num2/den2)));
plot(gamma,abs,'k.'); hold on
end
Or you can save the results and plot them outside the loop.
ncont=3.24;
kcont=4.28;
step=pi/180;
limit=2*pi;
gamma = 0:step:limit;
absv = zeros(size(gamma));
for k = 1:numel(gamma)
num1=(((ncont*cos(gamma(k)))-1)^2)+((kcont^2)*cos(gamma(k))^2);
num2=((ncont-cos(gamma(k)))^2)+kcont^2;
den1=(((ncont*cos(gamma(k)))-1)^2)+((kcont^2)*cos(gamma(k))^2);
den2=((ncont+cos(gamma(k)))^2)+kcont^2;
absv(k)=1-(0.5*((num1/den1)+(num2/den2)));
end
figure
plot(gamma,absv)
Of course, the loop isn't necessary either.
ncont=3.24;
kcont=4.28;
step=pi/180;
limit=2*pi;
gamma = 0:step:limit;
num1=(((ncont*cos(gamma))-1).^2)+((kcont^2)*cos(gamma).^2);
num2=((ncont-cos(gamma)).^2)+kcont^2;
den1=(((ncont*cos(gamma))-1).^2)+((kcont^2)*cos(gamma).^2);
den2=((ncont+cos(gamma)).^2)+kcont^2;
absv=1-(0.5*((num1./den1)+(num2./den2)));
figure
plot(gamma,absv)
