Before revision: Rathinam, M. and Murray, R. M., “Configuration flatness of Lagrangian systems underactuated by one control” SIAM Journal on Control and Optimization, 36, 164,1998. with pseudospectral method to generate outputs in the so-called flat space.
After revision: Rathinam, M. and Murray, R. M., “Configuration flatness of Lagrangian systems underactuated by one control” SIAM Journal on Control and Optimization, 36, 164,1998. with Pseudospectral optimal control to generate outputs in the so-called flat space.