[File: Boundary_condition_flag.txt]
Each node requires an input boundary condition flag.  It consists
of one digit per degree of freedom, and is denoted by the integer
array IBC within the program.

IBC (J) = Parameters constraint indicators at node J. (Right justified)
          Digit L equals constraint type of parameter L. (Default=0)

  NOTE: The IBC boundary condition indicator is an integer consisting
    of N_G_DOF digits that are constraint flags for the corresponding
    degrees of freedom at that node. The first DOF is the leftmost
    flag digit while the N_G_DOF-th DOF is the rightmost flag digit.  
    A zero denotes an unknown with no boundary conditions or constraint.
    Each digit can be from 0 to 9 but only 0,1,2,3 are supported now.
    Values other than 0 (free) or 1 (given value) rarely occur.

                  EXAMPLE, for N_G_DOF = 1
    IBC   Flag_1 Remarks
    0     0      One free unknown
    1     1      One type 1 constraint (assigned value)
    2     2      DOF is part of a type 2 constraint pair
    3     3      DOF is part of a type 3 constraint triplet

                  EXAMPLE, for N_G_DOF = 3
    IBC   Flag_1 Flag_2 Flag_3 Remarks
    000   0      0      0     Three free unknowns
    010   0      1      0     One type 1 constraint (assigned value)
    110   1      1      0     Two type 1 constraints (assigned values)
    002   0      0      2     DOF 3 has type 2 constraint
    022   0      2      2     DOF's 2 & 3 have type 2 constraint
    333   3      3      3     All coupled to type 3 constraint

The assigned value for each type 1 (essential) BC is given elsewhere
in the input.  Likewise, the linear constraint equation (MPC) for
each type 2 or 3 constraint is given elsewhere.

[End: Boundary_condition_flag.txt]