MS_POLYAVERAGE - Isotropic elasticity for polycrystal

Calculate the bulk and shear moduli of an isotropic polycrystal.

[ K_vrh, G_vrh, ... ] = MS_polyaverage( C )

Usage:
    [ K_vrh, G_vrh ] = MS_polyaverage( C )
        Return Voigt-Reuss-Hill average bulk (K) and shear (G) moduli of
        an isotropic aggregate composed of randomly orentated ansiotropic
        crystals described by the elasticity matrix C.

[ K_vrh, G_vrh, K_v, G_v, K_r, G_r ] = MS_polyaverage( C )
    Also return Voigt and Reuss bounds on the bulk and shear moduli.

Notes:
    For the case of an isotropic solid formed from a random distribution
    of elements, the bulk and shear moduli can be found directly without
    the need to rotate the crystal. See Anderson, Theory of the Earth,
    pp. 122.

See also: MS_VRH, MS_ANISOTROPY