This function does not belong to Matlab, but you can find it in the FileExchange. Asking Google for "VChooseKO" shows you the download page immediately as fist hit:
Use the download button to get the zip folder. Inside is the C-file, which must be compiled before using. Instructions are included.
Why do you search for this tool? Another user contacted me by email yesterday to ask where to find the C code of VChooseK and VChooseKR (the solution was easy: Use the download button). And a 3rd user could not find the C source of my RunLength submission yesterday also. Each question seems to be simple, but 3 equivalent problems in 24 hours are really strange.
