### Well Posed PDEs for Modeling Damped Strings

A large class of well posed PDEs is given by [45]

Thus, to the ideal string wave equation Eq.(C.1) we add any number of even-order partial derivatives in , plus any number of mixed odd-order partial derivatives in and , where differentiation with respect to occurs only once. Because every member of this class of PDEs is only second-order in time, it is guaranteed to be

*well posed*, as shown in §D.2.2.

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