MS_VRH - n phase Voigt-Reuss-Hill average of elasticity.

Given n elasticity matricies, densities and phase volume fractions,
    calculate the avarage of the Voigt upper and Reuss lower bound of the
    composite material.

[Cave,rhave]=MS_VRH(VF, C, rh, ...)

Usage:
    [Cave,rhave]=MS_VRH(VF, C, rh)
         The volume fractions and densities (VF and rh) can be provided as
         vectors of common length n and the elasticities as a (6,6,n)
         matrix.

[Cave,rhave]=MS_VRH(VF, C1, rh1, C2, rh2, C3, rh3, ...)
     Alternitivly, VF can be a vector of volume fractions and the
     elasticity matricies and densities given as sequence of arguments
     as (6,6) matricies and scalars. There should be a C,rho argument
     pair for each entry in the VF vector.

[Cave,rhave,Cvoigt,Creuss]=MS_VRH(VF, C, rh, ...)
     For both input argument forms, it is possible to access the upper
     and lower bound on the composite elasticity by adding output
     arguments.

Notes:
    The sum of the elements of VF is normalised to 1 before averaging.

See also: MS_POLYAVERAGE