If you instead installed Octave from the .zip archive, you need to first rebuild the package list on your local machine. (The command above will produce a blank output and packages will be inaccessible before rebuilding.) Do this by typing the following command:
>> pkg rebuild
''A bug in the Windows builds currently prevents Octave from automatically retrieving packages from the website for installation or updates. This will be fixed in the next Octave release. Until then, manual package installation is necessary to update or install new packages on Windows.''
To manually install a new or updated package version, the package file can be downloaded from the [https://octave.sourceforge.io/packages.php Octave-Forge website]to the working directory and can be installed using:
>> pkg install package_file_name.tar.gz
Detailed instruction of installing Octave-Forge packages is shown at [http://wiki.octave.org/Octave-Forge Octave-Forge]
== Octave 4.2.1 on cygwin==