Symmetry and positivity of a rigid-body resistance matrix ($\left(\genfrac{}{}{0ex}{}{\mathbf{F}}{\mathbf{G}}\right)=\mathsf{R}\left(\genfrac{}{}{0ex}{}{\mathbf{U}}{\mathbf{\Omega }}\right),{\mathsf{R}}^T=\mathsf{R},q^T\mathsf{R}q>0$)

Here $\mathbf{F},\mathbf{G}$ are forces and torques exerted by the body on the fluid, or the external force and torque needed to maintain its motion. The Lorentz reciprocal theorem for Stokes flow makes the six-dimensional hydrodynamic resistance matrix symmetric. The power identity $\mathbf{F}\cdot \mathbf{U}+\mathbf{G}\cdot \mathbf{\Omega }=2\mu \int e:edV$ makes it a positive-definite matrix for a body moving in otherwise stationary unbounded fluid.