At high frequencies the quadratic term becomes important.
This theory is nonlinear because of the quadratic terms in the strain-displacement relations.
The "interacting" part can very well also contain quadratic kinetic terms.
The quadratic terms in age were significant in both models though with opposite signs.
It is worth noting that the biting rate appears here as a quadratic term.
The same behavior can be obtained from the functional integrals, omitting the quadratic terms in the action.
The key schedule can be described by 1120 equations in 768 variables using 3328 linear and quadratic terms.
The entire block cipher can be described by 5104 equations in 2816 variables using 14592 linear and quadratic terms.
In total, 6224 equations in 3584 variables using 17920 linear and quadratic terms are required.
For specific forms of the quadratic term, this is a type of convex programming.