This is MATLAB's long-winded way of saying that it cannot find the function that you're trying to call. There are a number of reasons you could get this error:
The MATLAB online documentation provides a very nice feature which allows you to determine in what version a given function was introduced. It is located in the bottom left of every page of the documentation:
Compare this version with your own current version (
ver) to determine if this function is available in your particular version. If it's not, try searching the archived versions of the documentation to find a suitable alternative in your version.
The base MATLAB installation has a large number of functions; however, more specialized functionality is packaged within toolboxes and sold separately by the Mathworks. The documentation for all toolboxes is visible whether you have the toolbox or not so be sure to check and see if you have the appropriate toolbox.
To check which toolbox a given function belongs to, look to the top left of the online documentation to see if a specific toolbox is mentioned.
You can then determine which toolboxes your version of MATLAB has installed by issuing the
ver command which will print a list of all installed toolboxes.
If you do not have that toolbox installed and want to use the function, you will need to purchase a license for that particular toolbox from The Mathworks.
If MATLAB still can't find your function, then it must be a user-defined function. It is possible that it lives in another directory and that directory should be added to the search path for your code to run. You can check whether MATLAB can locate your function by using
which which should return the path to the source file.