### Index Analysis of Unsteady-State Chemical Process Systems--
I. An Algorithm for Problem Formulation

by

A. Lefkopoulos and M. A. Stadtherr

#### ABSTRACT

The convergence properties of the numerical methods used for solving
systems of differential/algebraic equations (DAEs) depend upon a very important
property of a DAE, its index. In general, index-one problems can be solved
routinely, while higher-index problems may present difficulties or be practically
unsolvable. The index of DAEs describing chemical processes is strongly
affected by the precise formulation of the problem, that is, by the choice
of independent variables and equations. Since these choices can often be
made rather arbitrarily, it is important that the index be made a criterion
in making this choice. In Part I of this set of two papers we present an
algorithm for selecting, whenever possible, the independent equations and
variables that lead to the formulation of an index-one DAE.

Comput. Chem. Eng., 17, 399-414 (1993)