POTHEA: A PROGRAM FOR COMPUTING EIGENVALUES AND EIGENFUNCTIONS AND THEIR FIRST DERIVATIVES WITH RESPECT TO THE PARAMETER OF THE PARAMETRIC SELF-ADJOINED 2D ELLIPTIC PARTIAL DIFFERENTIAL EQUATION ArticleGusev A.A., Chuluunbaatar O., Vinitsky S.I., Abrashkevich A.G.Computer Physics Communications. Том Vol 185. 2014.