|
| 1 | +<context> |
| 2 | +# Overview |
| 3 | +DualPerspective.jl is a Julia package that provides a novel approach to solving regularized optimization problems by reformulating them as instances of the regularized relative-entropy problem. The package transforms various problem classes (nonnegative least-squares, linear programming, optimal transport, and Hausdorff moment recovery) into a unified framework that exploits the conic extension of the probability simplex. |
| 4 | + |
| 5 | +The key innovation is the dual perspective approach that reformulates problems to have globally Lipschitz-smooth and strongly-convex objectives with uniformly bounded Hessian matrices, enabling efficient algorithms with strong convergence guarantees. |
| 6 | + |
| 7 | +# Core Features |
| 8 | +## Unified Problem Formulation |
| 9 | +- Reformulates various optimization problems as regularized relative-entropy problems |
| 10 | +- Leverages the conic extension of the probability simplex for nonnegative cone constraints |
| 11 | +- Provides a compactified problem formulation that enables efficient solution techniques |
| 12 | + |
| 13 | +## Dual Perspective Model (DPModel) |
| 14 | +- Extends AbstractNLPModel interface for seamless integration with Julia optimization ecosystem |
| 15 | +- Encapsulates data for regularized relative-entropy problems |
| 16 | +- Supports flexible regularization parameters and custom reference points |
| 17 | + |
| 18 | +## Advanced Optimization Algorithms |
| 19 | +- Trust-region Newton methods with quadratic convergence guarantees |
| 20 | +- Gauss-Newton solver with multiple linesearch strategies (Armijo-Goldstein, backtracking) |
| 21 | +- Level-set methods for constrained problems |
| 22 | +- Sequential scaling algorithms for improved numerical stability |
| 23 | + |
| 24 | +## Mathematical Foundations |
| 25 | +- Implements Kullback-Leibler divergence and its perspective transform |
| 26 | +- Provides primal and dual objective functions with analytical gradients and Hessians |
| 27 | +- Includes primal-from-dual solution mapping for recovering original variables |
| 28 | + |
| 29 | +## Cross-Language Support |
| 30 | +- Native Julia implementation for maximum performance |
| 31 | +- Python interface via JuliaCall for broader accessibility |
| 32 | +- MATLAB compatibility for researchers using legacy code |
| 33 | + |
| 34 | +# User Experience |
| 35 | +## Target Users |
| 36 | +- Researchers in optimization and computational mathematics |
| 37 | +- Machine learning practitioners working with regularized problems |
| 38 | +- Engineers solving large-scale transportation and resource allocation problems |
| 39 | +- Scientists requiring robust solutions to ill-conditioned inverse problems |
| 40 | + |
| 41 | +## Key User Flows |
| 42 | +1. **Problem Setup**: Users define their optimization problem using the DPModel constructor with constraint matrix A, target vector b, and optional parameters |
| 43 | +2. **Algorithm Selection**: Choose appropriate solver based on problem characteristics (Newton methods for smooth problems, Gauss-Newton for least-squares structure) |
| 44 | +3. **Solution Retrieval**: Obtain both primal and dual solutions with convergence diagnostics |
| 45 | +4. **Analysis**: Access detailed convergence metrics, optimality measures, and solution quality indicators |
| 46 | + |
| 47 | +## API Design Principles |
| 48 | +- Intuitive constructors that mirror mathematical notation |
| 49 | +- Consistent interface across different problem types |
| 50 | +- Comprehensive logging and debugging capabilities |
| 51 | +- Integration with Julia's optimization ecosystem (NLPModels.jl) |
| 52 | +</context> |
| 53 | +<PRD> |
| 54 | +# Technical Architecture |
| 55 | +## System Components |
| 56 | +### Core Models |
| 57 | +- `DPModel`: Main model type extending AbstractNLPModel |
| 58 | +- `OTModel`: Specialized model for optimal transport problems |
| 59 | +- `LPModel`: Linear programming with entropic regularization |
| 60 | +- `SSModel`: Self-scaling model variant |
| 61 | + |
| 62 | +### Objectives and Operations |
| 63 | +- Primal objective function with KL divergence regularization |
| 64 | +- Dual objective function with log-sum-exp operations |
| 65 | +- Value function computation for compactified problems |
| 66 | +- Gradient and Hessian computations with numerical stability |
| 67 | + |
| 68 | +### Solvers |
| 69 | +- Newton-CG: Newton method with conjugate gradient for linear systems |
| 70 | +- Newton-LS: Newton method with linesearch strategies |
| 71 | +- Gauss-Newton: Specialized solver for nonlinear least-squares structure |
| 72 | +- Sequential scaling: Adaptive scaling for improved conditioning |
| 73 | +- Level-set methods: Constraint-aware optimization |
| 74 | + |
| 75 | +### Utilities |
| 76 | +- Log-sum-exp implementations with numerical stability |
| 77 | +- Preconditioners for iterative solvers |
| 78 | +- Linear operators for matrix-free computations |
| 79 | +- Convergence diagnostics and logging |
| 80 | + |
| 81 | +## Data Models |
| 82 | +- Sparse and dense matrix support via SparseArrays.jl |
| 83 | +- Efficient storage of probability distributions |
| 84 | +- Lazy evaluation of Jacobian operators |
| 85 | +- In-place operations for memory efficiency |
| 86 | + |
| 87 | +## Infrastructure Requirements |
| 88 | +- Julia 1.6+ for modern language features |
| 89 | +- NLPModels.jl for optimization interface |
| 90 | +- Krylov.jl for iterative linear solvers |
| 91 | +- LinearOperators.jl for matrix-free operations |
| 92 | +- Logging.jl for configurable output |
| 93 | +- Test infrastructure with comprehensive coverage |
| 94 | + |
| 95 | +# Development Roadmap |
| 96 | +## Phase 1: Core Functionality Completion |
| 97 | +- Complete implementation of all solver variants |
| 98 | +- Finalize API for DPModel and related types |
| 99 | +- Implement remaining analytical properties (Hessian computations) |
| 100 | +- Add comprehensive error handling and input validation |
| 101 | +- Create extensive unit tests for all components |
| 102 | + |
| 103 | +## Phase 2: Documentation and Theory |
| 104 | +- Complete the theory.md documentation sections: |
| 105 | + - Convergence analysis with theoretical guarantees |
| 106 | + - Relationship to interior point and entropic regularization methods |
| 107 | + - Implementation details and algorithmic choices |
| 108 | + - Numerical experiments and benchmarks |
| 109 | +- Add docstrings to all exported functions and types |
| 110 | +- Create tutorial notebooks demonstrating key features |
| 111 | +- Write mathematical derivations for key algorithms |
| 112 | + |
| 113 | +## Phase 3: Performance Optimization |
| 114 | +- Profile and optimize hot paths in solver implementations |
| 115 | +- Implement specialized methods for structured problems |
| 116 | +- Add GPU support for large-scale problems |
| 117 | +- Create benchmark suite comparing to state-of-the-art solvers |
| 118 | +- Optimize memory allocation patterns |
| 119 | + |
| 120 | +## Phase 4: Advanced Features |
| 121 | +- Implement warm-start capabilities for sequential problems |
| 122 | +- Add support for box constraints and general convex sets |
| 123 | +- Create adaptive regularization strategies |
| 124 | +- Implement parallel variants for distributed computing |
| 125 | +- Add stochastic/incremental variants for large-scale problems |
| 126 | + |
| 127 | +## Phase 5: Integration and Ecosystem |
| 128 | +- Register package in Julia General registry |
| 129 | +- Create JuMP.jl extension for modeling interface |
| 130 | +- Integrate with Convex.jl for problem specification |
| 131 | +- Add Plots.jl recipes for visualization |
| 132 | +- Create interfaces to popular optimization benchmarks |
| 133 | + |
| 134 | +## Phase 6: Applications and Examples |
| 135 | +- Optimal transport examples with visualization |
| 136 | +- Machine learning applications (regularized regression, classification) |
| 137 | +- Image processing examples (denoising, deblurring) |
| 138 | +- Portfolio optimization with transaction costs |
| 139 | +- Network flow problems with congestion |
| 140 | + |
| 141 | +# Logical Dependency Chain |
| 142 | +## Foundation (Must be completed first) |
| 143 | +1. Core DPModel implementation with proper AbstractNLPModel interface |
| 144 | +2. Basic primal and dual objective functions |
| 145 | +3. Gradient computations with numerical stability |
| 146 | +4. Essential utility functions (log-sum-exp, KL divergence) |
| 147 | + |
| 148 | +## Core Algorithms (Depends on Foundation) |
| 149 | +1. Basic Newton method implementation |
| 150 | +2. Linesearch strategies for globalization |
| 151 | +3. Conjugate gradient for Newton systems |
| 152 | +4. Convergence criteria and stopping rules |
| 153 | + |
| 154 | +## Advanced Solvers (Depends on Core Algorithms) |
| 155 | +1. Gauss-Newton for least-squares structure |
| 156 | +2. Trust-region methods for robustness |
| 157 | +3. Sequential scaling for conditioning |
| 158 | +4. Level-set methods for constraints |
| 159 | + |
| 160 | +## Testing and Validation (Parallel with development) |
| 161 | +1. Unit tests for individual components |
| 162 | +2. Integration tests for complete workflows |
| 163 | +3. Numerical accuracy tests |
| 164 | +4. Performance benchmarks |
| 165 | + |
| 166 | +## Documentation and Examples (After Core Complete) |
| 167 | +1. API documentation with examples |
| 168 | +2. Mathematical theory documentation |
| 169 | +3. Tutorial notebooks |
| 170 | +4. Application examples |
| 171 | + |
| 172 | +## Distribution and Integration (Final Phase) |
| 173 | +1. Package registration |
| 174 | +2. Python interface finalization |
| 175 | +3. Continuous integration setup |
| 176 | +4. Community engagement |
| 177 | + |
| 178 | +# Risks and Mitigations |
| 179 | +## Technical Challenges |
| 180 | +- **Numerical Stability**: The log-sum-exp operations can suffer from overflow/underflow |
| 181 | + - Mitigation: Implement robust numerical techniques with careful scaling |
| 182 | + |
| 183 | +- **Convergence Issues**: Newton methods may fail for poorly conditioned problems |
| 184 | + - Mitigation: Implement robust globalization strategies and preconditioners |
| 185 | + |
| 186 | +- **Performance Bottlenecks**: Large-scale problems may be computationally intensive |
| 187 | + - Mitigation: Profile early and often, implement matrix-free operations |
| 188 | + |
| 189 | +## Algorithm Complexity |
| 190 | +- **Theoretical Guarantees**: Proving convergence for all problem classes |
| 191 | + - Mitigation: Focus on well-studied cases first, collaborate with theorists |
| 192 | + |
| 193 | +- **Parameter Selection**: Choosing appropriate regularization parameters |
| 194 | + - Mitigation: Implement adaptive strategies and provide guidance |
| 195 | + |
| 196 | +## Ecosystem Integration |
| 197 | +- **API Stability**: Changes may break dependent packages |
| 198 | + - Mitigation: Follow semantic versioning, maintain backwards compatibility |
| 199 | + |
| 200 | +- **Cross-Language Interface**: Python/MATLAB integration complexity |
| 201 | + - Mitigation: Start with minimal interface, expand based on user needs |
| 202 | + |
| 203 | +# Appendix |
| 204 | +## Mathematical Background |
| 205 | +The package implements the regularized relative-entropy problem: |
| 206 | +min_{x∈ℝⁿ₊} ⟨c, x⟩ + 1/(2λ)||Ax - b||²_{C⁻¹} + ∑ⱼ xⱼlog(xⱼ/x̄ⱼ) |
| 207 | + |
| 208 | +Key insight: ℝⁿ₊ = ⋃_{τ≥0} τΔⁿ where Δⁿ is the probability simplex |
| 209 | + |
| 210 | +## Related Work |
| 211 | +- Interior point methods for conic programming |
| 212 | +- Entropic regularization in optimal transport |
| 213 | +- Proximal methods for composite optimization |
| 214 | +- Trust-region methods for nonlinear optimization |
| 215 | + |
| 216 | +## Performance Targets |
| 217 | +- Solve medium-scale problems (n~10⁴) in seconds |
| 218 | +- Handle sparse problems with millions of variables |
| 219 | +- Achieve 1e-8 relative accuracy for well-conditioned problems |
| 220 | +- Scale linearly with problem size for structured problems |
| 221 | + |
| 222 | +## Testing Strategy |
| 223 | +- Unit tests achieving >90% code coverage |
| 224 | +- Integration tests for complete workflows |
| 225 | +- Stress tests for numerical stability |
| 226 | +- Performance regression tests |
| 227 | +- Comparison with established solvers (MOSEK, Gurobi for applicable problems) |
| 228 | +</PRD> |
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