“GLOBAL could be very inefficient”

Question

I am using (in Matlab) a global statement inside an if command, so that I import the global variable into the local namespace only if it is really needed.

Answer 1

To supplement eykanals post, this technical note gives an explanation to why global is slow.

... when a function call involves global variables, performance is even more inhibited. This is because to look for global variables, MATLAB has to expand its search space to the outside of the current workspace. Furthermore, the reason a function call involving global variables appears a lot slower than the others is that MATLAB Accelerator does not optimize such a function call.