APPENDIX A

 THE SIM DATA STRUCTURE



 Because each equation involved in the mathematical model of a

chemical process typically contains few of the variables involved in the

model, a special incidence matrix representation is desired for computer

applications. It is desired to store only the non-zero elements of the

incidence matrix, since they are the only elements of interest. These

incidence matrices, for obvious reasons, are called sparse incidence

matrices and the data structure employed to represent them is called the

SIM data structure. The SIM data structure was developed by Cunningham

(1973).

 The SIM is represented by five vectors, R, C, -i, V, and E. These

vectors are divided into cells. Each R-cell represents a row in the

SIM and each C-cell represents a column. The R- and C-cells all have

the same length, which may vary from application to application. The

usual length of R- and C-cells is six words. The contents of R- and C-

cells are interpreted as follows:

 R- or C- Cell

 Word Use

 1 Pointer to H- or V-cell

 2 Status Flag

 3 Various

 4 Output pointer