anchor.diff:  C
   C       =====================================================
   C       Purpose: Compute the initial characteristic value of
  -C                Mathieu functions for m  12  or q  300 or
  -C                q  m*m
  +C                Mathieu functions for m ≤ 12  or q ≤ 300 or
  +C                q ≥ m*m
   C       Input :  m  --- Order of Mathieu functions
   C                q  --- Parameter of Mathieu functions
   C       Output:  A0 --- Characteristic value
   C       Routines called:
   C             (1) CVQM for computing initial characteristic
  -C                 value for q  3*m
  +C                 value for q ≤ 3*m
   C             (2) CVQL for computing initial characteristic
  -C                 value for q  m*m
  +C                 value for q ≥ m*m
   C       ====================================================
   C
           IMPLICIT DOUBLE PRECISION (A-H,O-Z)
  
positive.code: C       Purpose: Compute the incomplete beta function Ix(a,b)
  C       Input :  a --- Parameter
  C                b --- Parameter
  C                x --- Argument ( 0  x  1 )
  C       Output:  BIX --- Ix(a,b)
  C       Routine called: BETA for computing beta function B(p,q)
  C       ========================================================
  
negative.code: C       ========================================================
  C       Purpose: Compute modified Bessel functions In(x) and
  C                Kn(x), and their derivatives
  C       Input:   x --- Argument of In(x) and Kn(x) ( x ≥ 0 )
  C                n --- Order of In(x) and Kn(x)
  C       Output:  BI(n) --- In(x)
  C                DI(n) --- In'(x)
  