Make the CORSIKA_DATA environment variable optional.
The CORSIKA_DATA location with data tables is of fundamental importance to run CORSIKA. It is very peculiar that so far we required users to define extra environment variables for this, and also corresponding error messages were not very good.
The default behavior should be that modules/data
is used to read the tables automatically and without intervention. User can still overwrite the default by providing a CORSIKA_DATA environment variable.
Edited by Ralf Ulrich