In this paper we present Affine.m - program for computations in
representation theory of finite-dimensional and affine Lie algebras and
describe implemented algorithms. Algorithms are based upon the properties of
weights and Weyl symmetry. The most important problems for us are the ones,
concerning computation of weight multiplicities in irreducible and Verma
modules, branching of representations and tensor product decomposition. These
problems have numerous applications in physics and we provide some examples of
these applications.
Recurrent relations for branching coefficients in affine Lie algebras
integrable highest weight modules are studied. The decomposition algorithm
based on the injection fan technique is adopted to the situation where the Weyl
denominator becomes singular with respect to a reductive subalgebra. We study
some modifications of the injection fan technique and demonstrate that it is
possible to define the "subtracted fans" that play the role similar to the
original ones. Possible applications of subtracted fans in CFT models are
considered.