This time I edited your question for you. Next time, please use the tools explained on this page to make your question more readable.
You can try putting a breakpoint at the start of your code and stepping through your code line by line. You can also step into a function call. That way you can make sure where your code hangs. It is very unlikely to be cause by the if or the comparison, however, you can verify this:
for i=1:3
a = Norm.Block(i).Rlong;
b = Norm.Block(i).Llong;
if a <= b
Coact.Block(i).RlongLlong=Norm.Block(i).Rlong/Norm.Block(i).Llong;
else
Coact.Block(i).RlongLlong=Norm.Block(i).Llong/Norm.Block(i).Rlong;
end
end
(the elseif can be replaced by else, as that condition is the exact opposite of the if)
