  Three object-oriented implementations of a prototype solver of the advection
equation are introduced. The presented programs are based on Blitz++ (C++),
NumPy (Python), and Fortran's built-in array containers. The solvers include an
implementation of the Multidimensional Positive-Definite Advective Transport
Algorithm (MPDATA). The introduced codes exemplify how the application of
object-oriented programming (OOP) techniques allows to reproduce the
mathematical notation used in the literature within the program code. A
discussion on the tradeoffs of the programming language choice is presented.
The main angles of comparison are code brevity and syntax clarity (and hence
maintainability and auditability) as well as performance. In the case of
Python, a significant performance gain is observed when switching from the
standard interpreter (CPython) to the PyPy implementation of Python. Entire
source code of all three implementations is embedded in the text and is
licensed under the terms of the GNU GPL license.
