A New Software Package For Linear Differential-Algebraic Equations

. We describe the new software package GELDA for the numerical solution of linear differential--algebraic equations with variable coefficients. The implementation is based on the new discretization scheme introduced in [20]. It can deal with systems of arbitrary index and with systems that do not have unique solutions or inconsistencies in the initial values or the inhomogeneity. The package includes a computation of all the local invariants of the system, a regularization procedure and an index reduction scheme and it can be combined with every solution method for standard index 1 systems. Nonuniqueness and inconsistencies are treated in a least square sense. We give a brief survey of the theoretical analysis of linear differential--algebraic equations with variable coefficients and discuss the algorithms used in GELDA. Furthermore, we include a series of numerical examples as well as comparisons with results from other codes, as far as this is possible. Key words. Differential-algeb..