output_file:

File name of desired output file (leave unset for no file output). $\;$
NOTE: This option only works when read from the ipopt.opt options file! An output file with this name will be written (leave unset for no file output). The verbosity level is by default set to "print_level", but can be overridden with "file_print_level". The file name is changed to use only small letters. The default value for this string option is "".
Possible values:

• *: Any acceptable standard file name