Type system

eOn was written to use Eigen as the matrix multiplication library. All matrices are row-major (eOnStorageOrder = Eigen::RowMajor), so that .data() yields [x0, y0, z0, x1, y1, z1, ...] as the Fortran potentials and VectorXd::Map round-trips expect.

Instead of the EIGEN_DEFAULT_TO_ROW_MAJOR preprocessor macro (which would make eOn’s Eigen types binary-incompatible with other libraries), client/Eigen.h provides explicit row-major type aliases (MatrixXd, Matrix3d, Matrix4d, AtomMatrix, RotationMatrix) alongside selective using declarations for vector types (VectorXd, VectorXi, Vector3d) that are unaffected by storage order.

Warning

New multi-dimensional Eigen matrix types in the codebase must use eOnStorageOrder or one of the existing row-major aliases. Adding a bare Eigen::MatrixXd (column-major) will silently corrupt force projections and data mapping.

Changed in version 2.11: Removed the EIGEN_DEFAULT_TO_ROW_MAJOR preprocessor macro. All matrix types are now explicitly row-major via aliases in client/Eigen.h, ensuring binary compatibility with other Eigen-based libraries.

Header conventions

Changed in version 2.x.

• include-what-you-use

• pragma once is preferred over setting ifdefs