Variables are either
sequential or nonsequential.
A variable is sequential if and only if any of the
following holds:
- it appears in a sequential COMMON block;
- it is a member of an aggregate variable group;
- it is an assumed-size array;
- it is a component of a derived type with
the Fortran 90 SEQUENCE attribute; or
- it is declared to be sequential in an HPF SEQUENCE
directive.
A sequential variable can be storage associated or
sequence associated; nonsequential variables cannot.
A COMMON block contains a sequence of components.
Each component is either an aggregate
variable group, or a variable that is not a member of any
aggregate variable group.
Sequential COMMON blocks contain a single component.
Nonsequential COMMON blocks may
contain several components that may be nonsequential or
sequential variables or aggregate variable groups.