This idea came up on the help mailing list, just noting it as I think it would be a useful enhancement. Note that it may end up being only corner cases, I'm not sure what percentage of functions fall into this category.

The missing_function_hook function _unimplemented_ has a list of known functions from Matlab and Matlab toolboxes, grouped by equivalent Octave package name, so it can tell users which package to load or install to get a given function.

This doesn't cover a couple cases: functions that should be in Octave core, but are in a package (e.g. xmlread in the io package); and functions that are in a package but are not in Matlab (e.g. assumptions in the symbolic package).

The _unimplemented_ function could be enhanced to search through the list of functions provided by installed packages, and show the user that a package could be loaded to be able to use that function.

Example showing how to locate a given function in the pkg cache structure:

>> assumptions
error: 'assumptions' undefined near line 1 column 1
>> pkgs = pkg ("describe", "all");
>> pkgs{5}.name
ans = symbolic
>> any (strcmp (pkgs{5}.provides{1}.functions, "assumptions"))
ans =  1