Octave has not implemented all of Matlab's functionality. You can see a list of Matlab functions that have not yet been implemented in Octave at the link below. It's a long list.

https://hg.savannah.gnu.org/hgweb/octave/file/tip/scripts/he...

EDIT: If the original link above isn't working, here's a fairly recent archived version:

https://web.archive.org/web/20250123192851/https://hg.savann...