Diagonal Riccati Stability and the Hadamard Product
  We present an extension of a recent characterisation of diagonal Riccati stability and, using this, extend a result of Kraaijevanger on diagonal Lyapunov stability to Riccati stability of time-delay systems. We also describe a class of transformations that preserve the property of being diagonally Riccati stable and apply these two results to provide novel stability results for classes of time-delay systems. 
Alexander Aleksandrov, Oliver Mason, Anna Vorob'eva
math.OC