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Optimal Control Capability

The SOCS software provides a general-purpose tool for solving optimal control problems. However, it is much more than just a sparse nonlinear programming package! Unique features include:

• Automatic Mesh Refinement -- Mesh points and discretization method are automatically chosen to satisfy user-specified solution accuracy.
• Alternate Discretizations -- Ten different discretization methods are available including Euler, Trapezoidal, Explicit Runge-Kutta, Hermite-Simpson, Linear multistep, and analytic propagation.
• Spline Solution -- The optimal solution (state and control) are represented as cubic B-splines, for easy interpolation and plotting.
• Direct Method -- It is not necessary to derive adjoint equations for most applications.
• Indirect Method -- If adjoint equations are available, SOCS can be used to solve the (multipoint) boundary value problem.
• Path Equality and Inequality Constraints -- SOCS accommodates general path constraints and does not require an a priori guess for constrained subarcs.
• Automatic Sparsity Determination -- The user does not need to define Jacobian and Hessian sparsity.
• Right-Hand Side Sparsity -- The sparsity of the user-specified differential (and algebraic) equations is automatically computed. This permits applications with hundreds of ODEs, including applications defined by partial differential equations.
• Sparse Finite Difference Derivatives -- SOCS automatically constructs the first and second derivatives for the user's application.
• Flexible Application Interface -- User provides software to evaluate the differential equations, path constraints and boundary conditions. SOCS does the rest!
• Multiple Phases -- SOCS can be applied to applications with multiple phases and/or paths.
• Diverse Applicability -- SOCS has been successfully applied to problems in
  • Aerospace trajectory design.
  • Robot and machine tool path design.
  • Chemical process control.
  • Distributed parameter control of partial differential equations (PDEs).
  • Chaotic differential equations.
  • Delay differential equations.
• Aerospace Trajectories -- SOCS has been fully integrated with:
  • the Optimal Trajectories by Implicit Simulation (OTIS 3.0) trajectory optimization package.
  • the Aerospace Trajectory Optimization Software (ASTOS)
• General Purpose Optimal Control, with graphical user interface to
  • the Graphical Environment for Simulation and Optimization (GESOP)
• Nonlinear Parameter Estimation -- permits solution of "inverse problems" involving measurement data at discrete time points. Its applications include
  • Orbit determination
  • Trajectory Reconstruction

Nonlinear Programming Capability

The key computational kernels of the SOCS library are the sparse nonlinear programming algorithms SPRNLP and BARNLP. For optimal control applications SPRNLP and BARNLP are fully integrated with the SOCS software and are transparent to the control practitioner. However, it is also possible to use SPRNLP and BARNLP independently for applications other than optimal control. The SPRNLP software implements a state-of-the-art sequential quadratic programming (SQP) method, using an augmented Lagrangian merit function and safeguarded line search. SPRNLP can accommodate nonlinear equality and inequality constraints, as well as simple bounds. The BARNLP software implements a sparse primal-dual interior point algorithm, in conjunction with a filter method for globalization. The outstanding performance of the software in benchmark tests has been documented. The package supports four different levels of functionality.

Sparse NLP

Provides general-purpose constrained optimization capability for very large applications. Unique features include:

• Sparse Quadratic Programming -- Schur-Complement QP Method needs only one sparse matrix factorization, even with active set changes!
• Primal-Dual interior point method efficient even with many inequality constraints.
• Sparse Linear Algebra -- Multifrontal solution of symmetric indefinite systems with pivoting for stability, using award-winning ¹ Boeing software BCSLIB-EXT.
• Arbitrary Jacobian and Hessian Sparsity -- Not restricted to block diagonal or other special form.
• Quadratic Convergence -- Efficient solution for very large problems. How large?
  • Variables≈500,000
  • Constraints≈500,000
• No Restriction on Degrees of Freedom. Unlike reduced Hessian methods, SPRNLP and BARNLP converge efficiently when the final active set is small or large.
• Reverse Communication Format -- Permits analytic and/or finite difference gradients.

Sparse Least Squares

Provides nonlinearly constrained least squares capability with all of the features of the general sparse NLP. Unique features include:

• Numerically Stable Solution -- Augmented QP format avoids formation of the normal matrix.
• Linear Least Squares -- Special option for linearly constrained (e.g., data fitting) applications

Dense NLP -- Simplified Usage

Provides general-purpose constrained optimization capability for small- to moderate- size applications with limited user requirements. Its features include:

• User Supplies Function Box -- SPRNLP or BARNLP does the rest!
• Hessian Options -- Quasi-Newton (SR1, BFGS, SSQN) and finite difference Newton.
• Finite Difference Jacobian/gradient.

Dense NLP -- Sophisticated Usage

Provides general-purpose constrained optimization capability for small- to moderate- size applications with more complex interface requirements. In addition to capabilities of the simplfied usage version, it uses a Reverse Communication Format that permits the user to supply Jacobian and optionally Hessian information.

Sparse Finite Difference Derivatives

In addition to the optimization tools, this package provides a collection of tools for computing first and second derivatives (Jacobian and Hessian) for sparse matrices. Unique features include:

• Number of perturbations much smaller than number of variables!
• Jacobian/Hessian Evaluation -- These procedures compute first and second derivative information using sparse differences.
• Index Set Construction -- Given matrix sparsity, this procedure determines how to group the variables for efficient differentiation.

Minimum Curvature Data Approxmiation

Multivariate tabular data can be approximated using tensor product spline functions. The software computes spline coefficients to:

• minimize the "wiggles" (curvature)
• interpolate and/or approxmiate table data

The software is fully integrated with the sparse nonlinear programming algorithms.

¹1988 Gordon Bell Award for High-Performance Computing

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