This package provides a modern C++17/ reimplementation of the UCMINF/ algorithm for unconstrained nonlinear optimization (Nielsen and Mortensen, 2011, <doi:10.32614/CRAN.package.ucminf>), offering full API compatibility with the original ucminf R package but developed independently. The optimizer core has been rewritten in C with a modern header-only C++17 interface, zero-allocation line search, and an Rcpp interface. The goal is numerical equivalence with improved performance, reproducibility, and extensibility. Includes extensive test coverage, performance regression tests, and compatibility checks against ucminf'. This package is not affiliated with the original maintainers but acknowledges their authorship of the algorithm and the original R interface.