[help-texinfo] Function Index: Index is nonexistent

[Lukas Reichlin]

Dear Texinfo Community,

I'm the author of GNU Octave's control package [1] and I'd like to create a 
function index for the package's PDF manual created from Texinfo source. 
However, the function index stays empty, only "Index is nonexistent" is 
displayed. What can I do to populate the function index with the functions 
marked with @findex foobar?

The corresponding files are to found in the SVN repository [2], control.tex is 
the main file, functions.texi contains the functions with the @findex commands, 
and control.pdf is the current output with empty index.

Thanks for any help and best regards,
Lukas


[1]
http://octave.sourceforge.net/control/index.html


[2]
https://sourceforge.net/p/octave/code/11159/tree/trunk/octave-forge/main/control/devel/pdfdoc/