Text this: Henrici's transformation and its application to the computation of derivatives of eigensystems

           __   __   ______    __   __    ______  
    ___    \ \\/ // |      \\  \ \\/ //  /_   _// 
   /   ||   \ ` //  |  --  //   \ ` //   `-| |,-  
  | [] ||    | ||   |  --  \\    | ||      | ||   
   \__ ||    |_||   |______//    |_||      |_||   
    -|_||    `-`'   `------`     `-`'      `-`'   
     `-`