Gradient flow with diagonal mobility (source code)

= Gradient flow with diagonal mobility
{title2=$\dot x_r=m_r(x)\partial_rU$}

Positive mobility coefficients $m_r(x)$ give $dU/dt=\sum_rm_r(x)(\partial_rU)^2\geq0$. With $m_r=\kappa_rx_r$, the substitution $z_r=2\sqrt{x_r/\kappa_r}$ turns the equation into ordinary gradient ascent for the transformed potential on positive coordinates.