I finally understood your problem. The problem description needs some adjustment. It is not clear that it is requesting only the global variable named 'z'. I thought it was referring to every global variable.
The Hitchhiker's Guide to MATLAB
Volume difference between Ellipsoid and Sphere
Insert zeros into vector
Moving average (variable kernel length)
Comparison of floating-point numbers (singles)
Testing for randomness: uniform distribution of real numbers (distribution checking)
Add all the numbers between two limits (inclusive)
Make your own Test Suite (part 1)
Rate of event occurence: find percentiles of the distribution (for smallish rates)
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