Pseudospectral knotting method
{{Short description|Optimal control technique}}
In applied mathematics, the pseudospectral knotting method is a generalization and enhancement of the standard pseudospectral method for optimal control. Introduced by I. Michael Ross and F. Fahroo in 2004, it forms part of the collection of the Ross–Fahroo pseudospectral methods.Ross, I. M. and Fahroo, F., Pseudospectral Knotting Methods for Solving Optimal Control Problems, Journal of Guidance, Control and Dynamics, Vol. 27, No. 3, pp. 397–405, 2004.
Definition
According to Ross and Fahroo, a pseudospectral (PS) knot is a double Lobatto point; i.e. two boundary points coinciding. At this point, information (such as discontinuities, jumps, dimension changes etc.) is exchanged between two standard PS methods. This information exchange is used to solve some of the most difficult problems in optimal control, known as hybrid optimal control problems.Ross, I. M. and D’Souza, C. N., A Hybrid Optimal Control Framework for Mission Planning, Journal of Guidance, Control and Dynamics, Vol. 28, No. 4, July–August 2005, pp. 686–697.
In a hybrid optimal control problem, an optimal control problem is intertwined with a graph problem. A standard pseudospectral optimal control method is incapable of solving such problems; however, through the use of pseudospectral knots, the graph information can be encoded at the double Lobatto points, thereby allowing a hybrid optimal control problem to be discretized and solved using powerful software such as DIDO.
Applications
PS knots have found applications in various aerospace problems such as the ascent guidance of launch vehicles and advancing the Aldrin Cycler using solar sails.Stevens, R. and Ross, I. M., Preliminary Design of Earth–Mars Cyclers Using Solar Sails, Journal of Spacecraft and Rockets, Vol. 41, No. 4, 2004. Stevens, R., Ross, I. M. and Matousek, S. E., "Earth-Mars Return Trajectories Using Solar Sails," 55th International Astronautical Congress, Vancouver, Canada, IAC-04-A.2.08, October 4–8, 2004.
PS knots have also been used for anti-aliasing of PS optimal control solutions and for capturing critical information in switches when solving bang-bang-type optimal control problems.Gong, Q., Fahroo, F. and Ross, I. M., A Spectral Algorithm for Pseudospectral Methods in Optimal Control, Journal of Guidance, Control and Dynamics, Vol. 31, No. 3, pp. 460–471, 2008.
Software
The PS knotting method was first implemented in the [https://www.mathworks.com/products/connections/product_detail/product_61633.html MATLAB optimal control] software package, DIDO.
See also
References
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