MATLAB: If/Else statement within a For loop statement

Question

% OBJ: Clear command window and workspace

clear

clc

% OBJ: Create the vector of angles theta

theta=[-pi/2: pi/100: pi/2];

% OBJ: Calculate gain for each angle theta

for G=[theta];

if theta==0

G=0.5;

else

G=abs((sin(4.*theta))./(4.*theta));

end

end

% OBJ: Create and display a polar plot of G vs. theta

polar(theta,G)

title('Antenna Gain vs. Theta')

The reason I have to do this is to account for the point where theta will equal 0 and leave that data point undefined but idk why the data point remains undefined. When I run the script, everything is correct and the graph looks good, except for that one data point which remains undefined.

There's something wrong syntactically in the loop, but I cannot ascertain what it is. Any help is appreciated.

Answer 1

First, the easy way:

 theta=[-pi/2: pi/100: pi/2];
G=abs((sin(4.*theta))./(4.*theta));
G(theta==0) = 0.5
polar(theta,G)

Second, the reason your loop isn't working is because you redefine G on each iteration. You need to index into the iith element of G

for ii = 1:n
 if theta(ii)==0
    G(ii) = 0.5
 else
    G(ii) = stuff_with(theta(ii))
 end
end