MS_VTI2

MS_VTI2 - generate elastic constants for a vertically transverse isotropic
            medium from xi, phi, eta parameters. Symmetry is in the 3-axis.
[C]=MS_VTI2(vp,vs,rh,xi,phi,eta)
Inputs:
    rh  : Density (kg/m2)
    vp  : km/s (isotropic average)
    vs  : km/s (isotropic average)
    xi, phi, eta : Dimensionless anisotropy parameters
Output:
     C : Stiffness tensor (6x6 notation, GPa)
See also: MS_VTI, MS_iso, MS_elasticDB