  We introduce COLOSS, a program designed to address the scattering problem
using a bound-state technique known as complex scaling. In this method, the
oscillatory boundary conditions of the wave function are transformed into
exponentially decaying ones, accommodating the long-range Coulomb interaction.
The program implements the Woods-Saxon form of a realistic optical potential,
with all potential parameters included in a well-designed input format for ease
of use. This design offers users straightforward access to compute
\(S\)-matrices and cross-sections of the scattering process. We provide
thorough discussions on the precision of Lagrange functions and their benefits
in evaluating matrix elements. Additionally, COLOSS incorporates two distinct
rotation methods, making it adaptable to potentials without analytical
expressions. Comparative results demonstrate that COLOSS achieves high accuracy
when compared with the direct integration method, Numerov, underscoring its
utility and effectiveness in scattering calculations.
