Even if a were 1, so that both “branches” were the same, this is non-convex. See Cvx expression divide problem . No matter how many times you ask or how badly you want it to be convex, it is not.
Even if a were 1, so that both “branches” were the same, this is non-convex. See Cvx expression divide problem . No matter how many times you ask or how badly you want it to be convex, it is not.