Are augmentData and preprocessData in the same file (and a different file than the one in which you're trying to use preprocessData?) As stated in the documentation in a function file only the main (first) function is directly callable outside the file.
"Program files can contain multiple functions. If the file contains only function definitions, the first function is the main function, and is the function that MATLAB associates with the file name. Functions that follow the main function or script code are called local functions. Local functions are only available within the file."
The easiest approach, if you want to use preprocessData in multiple files or from the Command Window, is to make it its own main function in its own function file.
