Eigen solution with Number class to compile

[ohhmm]

No description provided.

[devin-ai-integration]

Multiple issues found in the Eigen integration:

1. The Number type is undefined but used in using extrapolator_base_matrix = Eigen::Matrix<Number, Eigen::Dynamic, Eigen::Dynamic>;
2. The header file "Expression.h" is included but doesn't exist in the codebase
3. The CMake configuration for Eigen is causing build failures - the repository URL https://github.com/libeigen/eigen.git is incorrect or inaccessible

Recommendations:

• Define the Number type or use an existing type like Valuable or a numeric type
• Remove the non-existent "Expression.h" include
• Fix the Eigen repository URL in CMake configuration or use vcpkg properly

[devin-ai-integration]

The Extrapolator class has conflicting base class definitions:

// First definition
using extrapolator_base_matrix = boost::numeric::ublas::matrix<extrapolator_value_type>;

// Second definition that overwrites the first
using extrapolator_base_matrix = Eigen::Matrix<Number, Eigen::Dynamic, Eigen::Dynamic>;

This creates confusion and compilation errors. You should:

1. Choose one implementation (either boost::ublas or Eigen)
2. If transitioning to Eigen, update all related code consistently
3. Remove the commented-out code that's no longer needed

[devin-ai-integration]

The implementation of Solve method has several issues:

1. There's a duplicate implementation of Solve - one is declared but not defined, and another is defined inline
2. The inline implementation uses Eigen's llt() method but returns solution.rhs() which doesn't match the expected return type
3. The method doesn't handle potential errors in matrix solving

Recommendation: Consolidate the two implementations into one correct implementation that properly handles errors and returns the expected type.