@classmethod
def from_comp(cls, xx=1, xy=0, xz=0, yy=1, yz=0, zz=1, **kwargs) ->'Tensor':
    """
        Return tensor. Default is identity tensor.

        Note that tensor must be symmetrical.
        """
    return cls([[xx, xy, xz], [xy, yy, yz], [xz, yz, zz]], **kwargs)
