Solution set

In mathematics, a solution set is the set of values that satisfy a given set of equations or inequalities. For example, for a set {f_i} of polynomials over a ring R, the solution set is the subset of R on which the polynomials all vanish (evaluate to 0), formally {x\in R: \forall i\in I, f_i(x)=0} The feasible region of a constrained optimization problem is the solution set of the constraints. The solution set of the single equation is the set {0}. For any non-zero polynomial over the complex numbers in one variable, the solution set is made up of finitely many points. However, for a complex polynomial in more than one variable the solution set has no isolated points. In algebraic geometry, solution sets are called algebraic sets if there are no inequalities. Over the reals, and with inequalities, there are called semialgebraic sets. More generally, the solution set to an arbitrary collection E of relations (Ei) (i varying in some index set I) for a collection of unknowns , supposed to take values in respective spaces , is the set S of all solutions to the relations E, where a solution is a family of values such that substituting by in the collection E makes all relations "true". (Instead of relations depending on unknowns, one should speak more correctly of predicates, the collection E is their logical conjunction, and the solution set is the of the boolean value true by the associated boolean-valued function.) The above meaning is a special case of this one, if the set of polynomials fi if interpreted as the set of equations fi(x)=0. The solution set for E = { x+y = 0 } with respect to is S = { (a,−a) : a ∈ R }. The solution set for E = { x+y = 0 } with respect to is S = { −y }. (Here, y is not "declared" as an unknown, and thus to be seen as a parameter on which the equation, and therefore the solution set, depends.) The solution set for with respect to is the interval S = [0,2] (since is undefined for negative values of x). The solution set for with respect to is S = 2πZ (see Euler's identity).