A few points to note:
1. "for k = length(CG_X)" would assign only a single value of 10 to 'k'. You need 'k' to take all values from 1 to 10.
2. While checking the condition in if-statement, you want to check the value of an element in CG_X indexed by k, not k itself.
3. "plot(CG_X,CG_Y,'r*');" would plot all the points in one go in red color. You need to plot only one point in each run of the for loop.
The following code incorporates the above mentioned changes:
CG_X=[13.8 18 18.8 -5.7 2.2 -11.1 -6.3 12.4 -10.5 15.6];
CG_Y=[4.2 -13.2 -8 -11.3 11.2 1.5 -5.0 8 -7.1 19.7];
hold on;
for k=1:length(CG_X)
if CG_X(k)>15||CG_X(k)<-15
plot(CG_X(k),CG_Y(k),'r*');
else
plot(CG_X(k),CG_Y(k),'b*');
end
end
hold off;
