1. Some Explicit Formulas for the Exponential Matrix e tA
2. BARNETT , S. , and CAMERON , R. G. , 1985 ,Introduction to Mathematical Control Theory, second edition ( Oxford Clarendon Press ), Chap. 4 , 2 .
3. Matrix exponential: Approximation by truncated power series
4. DUNFORD , N. , and SCHWARTZ , J. T. , 1958 ,Linear Operators, Part I ( New York Intcrscience ), p. 560 .