Tearing is the process of choosing the set of feedback marks that if
removed from the matrix (and then the matrix is re-partitioned) will render
the matrix lower triangular. The marks that we remove from the matrix are
called "tears".
Identifying those "tears" that result in a lower triangular matrix means that we have identified the set of assumptions that need to be made in order to start design process iterations when coupled tasks are encountered in the process. Having made these assumptions, no additional estimates need to be made.
No optimal method exist for tearing, but we recommend the use of two criteria when making tearing decisions:
· Minimal number of tears: the motivation behind this criterion is that tears represent an approximation or an initial guess to be used; we would rather reduce the number of these guesses used.
· Confine tears
to the smallest blocks along the diagonal: the motivation behind this criterion is that if there are to be iterations within iterations (i.e. blocks within blocks), these inner iterations are done more often. Therefore, it is desirable to confine the inner iterations to a small number of tasks.
