Subject: Permafrost (PermFrst) option

Name: Lance David

Date: 06/17/2019

Variants affected: AK variant

Description: The diameter growth equations in the new AK varaint has a
             permafrost modifier option that is unique and not applicable
             to any other variant. A new keyword and schedulable activity
             has been added, PermFrst. The default condition of the
             modifier is inactive. Change to this active or inactive
             status remains in affect until that status is changed at a
             later date in the projection. The keyword has two fields,
             date and modifier status (0 = inactive and 1 = active). If
             the date in PermFrst keyword field 1 is 0 or blank, modifier
             status will be set as specified without the scheduling of an
              activity.

Impact on users: New and unique control for AK diameter growth.
                 
Files:

ak/.f
base/grincr.f     - Added PermFrst activity processing.
base/keywds.f     - Added PERMFRST keyword to table.
base/optilst.f    - Added PermFrst option (keyword 146, activity code 445)
common/CONTRL.f77 - Added logical variable LPERM for AK variant permafrost
                    modifier control.
vbase/initre.f    - Added processing of new PermFrst keyword.
