Set default values as a function/query in Crystal Reports

Hi,

Is it possible to set default values as a function or a query for a command object parameter in CR2013?

I have two parameters in my report:

From_date & To_date

I need the From_date to be a week ago from today and the To_date to be yesterday.

I would ideally want them to be already set when the user opens the report.

                                                     OR

If the user does not provide a value for these parameters, the defaults should be set.

Any help you can give would be appreciated.

Regards.