AN EQUATION ANALYZER FOR PROCESS MODELS

We discuss an equation analyser which analyses matrix structure to det ect incorrect specification in equation systems and identifies free va riables. Structural analysis uses output assignment to find a trial se t of free variables. The choice is affected by the rules for output va riable selection in each equation and to a lesser extent by how the eq uations are reordered. Numerical singularity is found by attempting Ga ussian elimination of the initial Jacobian. Causes include dependent e quations or an unsuitable starting guess. Element type codes distingui sh constant and variable Jacobian elements. Rules for element type ari thmetic are presented. The equation analyser cannot distinguish a sing ular guess from nonlinear dependence, which may be detected if singula rity persists in a partial solution at later iterations. We show the f ree variable choices and ease of solution for the corresponding simula tions are presented in three examples with between 22 and 60 variables . Rules for equation ordering and output variable assignment are propo sed. (C) 1998 Elsevier Science Ltd. All rights reserved.