@article{biehn_campbell_jay_westbrook_2000, title={Some comments on DAE theory for IRK methods and trajectory optimization}, volume={120}, ISSN={["0377-0427"]}, DOI={10.1016/S0377-0427(00)00306-X}, abstractNote={It has been observed elsewhere in the literature that the activation of constraints in a trajectory optimization problem can lead to higher index DAEs. Several existing codes can handle a number of these constrained problems. In this note we will discuss why the situation is more complex than just saying a higher index DAE occurs. The discussion is in the context of a specific industrial code SOCS but the observations made here have relevance for a number of methods and have implications for what types of test problems a code should be tested on.}, number={1-2}, journal={JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS}, author={Biehn, N and Campbell, SL and Jay, L and Westbrook, T}, year={2000}, month={Aug}, pages={109–131} }