traj_gen is a continuous trajectory generation package where high order derivatives along the trajectory are minimized while satisfying waypoints (equality) and axis-parallel box constraint (inequality). The objective and constraints are formulated in quadratic programming (QP) to cater the real-time performance.
To parameterize a trajectory, we use two types of curve: 1) piecewise-polynomials [1,2] and 2) a sequence of points . The difference is optimization variables.
a. Piecewise-polynomials (polyTrajGen class) : It defines the primitive of the curve as polynomical spline. The optimization target is either polynomial coefficients  or free end-derivatives of spline segments  (can be set in constructor). In general, the latter has fewer optimization variables as it reduces the number of variable as much as the number of equality constraints.
b. A sequence of points (optimTrajGen class) : It does not limit the primitive of the curve. The optimization target is a finite set of points. The final curve is defined as a linear interpolant of the set of points. The point density (# of points per time) should be set in the constructor. Instead of unlimited representation capability of a curve, the size of optimization is driectly affected by the point density.
In this package, we use pin to accommodate the two constraints: equality (fix pin) and inequality (loose pin). Pin can be imposed regardless of the order of derivatives. Fix-pin refers a waypoint constraint, and loose-pin denotes a axis-parallel box constraint. The pin is a triplets (time (t), order of derivatives (d), value (x)) where x is a vector in case of fix-pin while two vectors [xl xu] for the loose-pin.
 Mellinger, Daniel, and Vijay Kumar. "Minimum snap trajectory generation and control for quadrotors." 2011 IEEE International Conference on Robotics and Automation. IEEE, 2011.
 Richter, Charles, Adam Bry, and Nicholas Roy. "Polynomial trajectory planning for aggressive quadrotor flight in dense indoor environments." Robotics Research. Springer, Cham, 2016. 649-666.
 Ratliff, Nathan, et al. "CHOMP: Gradient optimization techniques for efficient motion planning." 2009 IEEE International Conference on Robotics and Automation. IEEE, 2009.
boseong jun (2021). traj_gen-matlab (https://github.com/icsl-Jeon/traj_gen-matlab), GitHub. Retrieved .
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