The real complexity arises for many different reasons:
1. Coupling of FRs
2. Decrease in the allowable tolerance due to the
presence of coupling terms (i.e., the off-diagonal terms in
[DM]) - see Appendix A
3. Lack of robustness (i.e., too large 'stiffness') - See
Appendix A
4. Wrong choice of DPs
5. Wrong decomposition of FRs and DPs