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My testing indicates this is slower than interp2 for Matlab R2013a.
Thanks for your submission. For my tastes, Matlab takes a rather narrow view of what is "built-in", though (e.g., xlabel() is not built-in according to Matlab).
I tweaked the code trivially to do the following:
1. Include the full search path (except for demos)
2. Label anything under the matlabroot directory structure as built-in.
This way my own functions on the path are labeled one way and Matlab's functions are labeled another.