That's how all builtin functions work in Matlab, that's why they're "built in"; the working part of the function is compiled code built into the executable for the program. Core functionality is incorporated in that manner to improve performance; other routines are just supplied m-code no different than user-written as far as their implementation. There are also p-code and mex files...
Why do you think you need to include the function in some other location; there really is no reason to do that in general. Occasionally one will take a specific m-file and create a slightly modified version for a specific purpose, but it's highly recommended to make the user copy distinct and to not modify nor alias actual distributed functions.
Best Answer