Resolved: cubics, quartics and quintics At the moment, tag quadratic-equation is a synonym for tag quadratics. Hence, I propose that cubic-equations ⟶ cubics quartic-equations ⟶ quartics Say, on a question on the number of real roots of a given cubic polynomial, I would rather see tag cubic...

I have a relatively standard optimal quadratic control problem on infinite horizon : $\int_0^\infty R^\top R + R^\top Q u + u^\top Q u~ dt $ subject to $\dot R = kR - u $ but with one specific. $R$ is artificially constructed from integral $$ R = \int_x^\infty e^{k(x-t)} u(t) dt $$ That means ...