MS_CHECKC - check consistency of a stiffness matrix against various criteria

[ isgood ] = MS_checkC( C,... )

   Inputs:
C = Stiffness tensor for checking

Outputs:
   isgood = 1 for OK

Options:
   Various checks can be disabled/enabled by specifying extra options:
      'fast' - run a minimal set of checks (size and type only)
      'warn' - warn only on more sophisticated errors than size/type
      'nosymchk' - disable upper, lower symmetry checking
      'nozerochk' - disable top left / trace zero checking
      'nopdefchk' - disable positive definiteness check

Various control parameters can be set by adding parameter,value pairs
to the arguments
   'thresh',x - set numerical threshold for zero to x (default = 1e-6)

Notes:
Currently, the following properties of the input elastic stiffness
matrix, C, are tested: (1) The maxtrix must be of rank 2 and size (6,6).
(2) The matrix must be symmetrical along the leading diagonal (i.e.
the major symmetry of the elastic constants tensor, Cijkl == Cklij, must
be present). (3) The matrix must be positive-definite and be none zero
in the leading diagonal and top left corner.