Group Expressions

Several of the POLPACK applications have parameters which are described as being associated with groups (or lists) of objects. For instance, the POLKA parameter ``IN'' specifies a group of input data files, and the POLPLOT parameter ``STYLE'' specifies a group of plotting attributes. A group expression is the string typed in by the user in response to a prompt for such a parameter. It should identify the members of the required group in any of the following ways:

• As a comma separated list ( e.g. ``12.1, 23.2, 1.3'' or ``HH1_B1S1,HH2_B1S2'' ).

• By reading them from a text file (see ``Indirection'').

• By modifying an existing group of objects using editing specified within the group expression (see ``Modification'').

If the supplied group expression is terminated with a minus sign, the user is re-prompted for another group expression. The objects specified by this second group expression are added to those specified by the first. This re-prompting continues until a group expression is supplied which does not end with a minus sign.

Certain classes of objects have additional features, for instance if the objects are the names of data files, then wild-card characters are allowed in the supplied values (see here)