1. A computer implemented method for solving a parametric multi-objective optimization problem in a combined design space and parameter space using interval techniques, wherein the design space contains design-space variables which are fixed for a selected design, and wherein the parameter space contains parameters which are variables for the selected design, the method comprising: receiving a design-optimization problem at a computer system, wherein the problem is specified by multiple-objective functions which are to be optimized in the combined design space and parameter space; initializing, using the computer system, a design-variable box spanning the design space; performing, using the computer system, an interval optimization process on the parameter space by subdividing the design-variable box in the design space into design-variable sub-boxes, and: determining, using the computer system, a parametric Pareto front for a design-variable sub-box using an interval optimization technique; comparing, using the computer system, a set of parametric Pareto fronts associated with a set of design-variable sub-boxes to determine which parametric Pareto fronts are certainly dominated by other parametric Pareto fronts; eliminating, using the computer system, the design-variable sub-boxes associated which the parametric Pareto fronts which are certainly dominated by other parametric Pareto fronts; and if predetermined stopping criteria are not met: subdividing remaining design-variable sub-boxes; and repeating the determining, comparing and eliminating steps; otherwise: producing, using the computer system, an optimized solution for the design-optimization problem from the remaining design-variable sub-boxes and the associated parametric Pareto fronts.