[File: Extending_Sys_Constants.txt]
              
                   Extending System Constants

New applications of the MODEL code may need to define new system 
constants (integer, logical, or real), and the ability to input them.  
They can be input through the "keywords" facility, and inserted into 
the code by the following steps:

1. A) Edit Use_module_lib.f and insert the names in the data section of
   that module.  If values are to be set, or recovered by subprograms 
   then also add such routines to the functionality section of the 
   module (that is, after the CONTAINS line). Usually initial values 
   will be set with the "keywords" facility.

   B) You always should edit the subroutine SET_CONTROL_DEFAULTS to set
   a default value for the variable and to comment its purpose.

2. Edit Notation.F to list the variable and comment its purpose.

3. A) In keyword_lib.f edit subroutine apply_key to accept the new 
   control variable name, and/or a corresponding keyword, and then set 
   its value or call needed routines.

   B) Edit the help file Keword_input.txt to list the new keyword, its
   default value (set in step 1.A), and its description.

After these changes you can access the new control variable (and change
it) by including the Use System_Constants line in your programs.

[End File: Extending_Sys_Constants.txt] 1/9/01