5. Process Improvement
5.5. Advanced topics
5.5.3. How do you optimize a process?
5.5.3.1. Single response case

5.5.3.1.6.

Single response: Optimization subject to experimental region constraints

Optimal operating conditions may fall outside region where experiment conducted

Sometimes the optimal operating conditions x^* simply fall outside the region where the experiment was conducted. In these cases, constrained optimization techniques can be used to find the solution x^* that optimizes $\hat{Y}(x)$ without leaving the region in the factor space where the experiment took place.

Ridge analysis is a method for finding optimal factor settings that satisfy certain constraints

"Ridge Analysis", as developed by Hoerl (1959), Hoerl (1964) and Draper (1963), is an optimization technique that finds factor settings x^* such that they

$\text{optimize}\hat{Y}(x)=b_0+b^{\prime }x+x^{\prime }Bx$

$\text{subject to}{x}^{\prime }x={\rho }^2$

The solution x^* to this problem provides operating conditions that yield an estimated absolute maximum or minimum response on a sphere of radius ρ. Different solutions can be obtained by trying different values of ρ.

Solve with non-linear programming software

The original formulation of Ridge Analysis was based on the eigenvalues of a stationarity system. With the wide availability of non-linear programming codes, Ridge Analysis problems can be solved without recourse to eigenvalue analysis.