MATLAB has toolbox cache which contains a list of all of the files located in the toolbox directories ($MATLABROOT$\toolbox) and all of their subdirectories. If a function is already in memory, MATLAB uses the cache on subsequent calls to the function. It is faster for MATLAB to run the files from the cache than it is to reload the files. The cache is used for toolbox directories because they should not be changing very often (if at all).
After MATLAB 6.0 (R12), when a file is saved and if that file is located in $MATLABROOT$\toolbox, toolbox cache is updated to reflect the latest version of the file. So when you run the file next time, it should reflect the changes.
If for some reason the changes are not reflected, you can force MATLAB to reload the function into cache. In order to force MATLAB to reload the function, use the CLEAR command to clear the function from memory. For example, the following code will clear 'myfcn' from memory:
clear myfcn
After 'myfcn' has been cleared from memory, the next use of 'myfcn' will force MATLAB to reload the file.
If you have changed the contents of the toolbox directories (adding/removing directories or files), then you can use the REHASH command to force MATLAB to update the toolbox cache file. For example:
rehash toolboxcache
