@article{biehn_campbell_nikoukhah_delebecque_2001, title={Numerically constructible observers for linear time-varying descriptor systems}, volume={37}, ISSN={["0005-1098"]}, DOI={10.1016/S0005-1098(00)00168-0}, abstractNote={This paper examines the design of observers for linear time-varying descriptor systems. An observer is designed for which the observer estimates are also physically correct in that they satisfy the same constraints as the solutions of the descriptor system. Careful attention is paid to ensuring that all quantities are computable by numerical algorithms. One way to implement this approach is fully developed. A computational example is given.}, number={3}, journal={AUTOMATICA}, author={Biehn, N and Campbell, SL and Nikoukhah, R and Delebecque, F}, year={2001}, month={Mar}, pages={445–452} }
 @article{betts_biehn_campbell_huffman_2000, title={Compensating for order variation in mesh refinement for direct transcription methods}, volume={125}, ISSN={["0377-0427"]}, DOI={10.1016/S0377-0427(00)00465-9}, abstractNote={The numerical theory for Implicit Runge–Kutta methods shows that there can be order reduction when these methods are applied to either stiff or differential algebraic equations. This paper discusses how this theory can be utilized in direct transcription trajectory optimization by modifying a currently used mesh refinement strategy.}, number={1-2}, journal={JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS}, author={Betts, JT and Biehn, N and Campbell, SL and Huffman, WP}, year={2000}, month={Dec}, pages={147–158} }
 @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} }