A matrix that translates original inertia matrix by delta $\vec{r}$. Computed as the following. $$\mathcal{I}_r = \left[\begin{array}{ccc} r_y^2+r_z^2 & -r_xr_y & -r_xr_z \\ -r_xr_y & r_x^2+r_z^2 & -r_yr_z \\ -r_xr_z & -r_yr_z & r_x^2+r_y^2 \\ \end{array}\right]$$ Here $\vec{r}$ is a vector from the original centre of mass to the new centre of mass.

Inertia matrix in body-fixed coordinate system. Inertia matrix $\mathcal{I}$ is calculated from inertia tensor $I$ as follows: $$\mathcal{I} = \left[\begin{array}{ccc} I_x & -I_{xy} & -I_{xz} \\ -I_{yx} & I_y & -I_{yz} \\ -I_{zx} & -I_{zy} & I_z \end{array}\right].$$