Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:The selected test set contains 29 small-scale equality-constrained optimization problems used by Colson [1] in his numerical tests, and our results are compared to those obtained with the software CDFO in this reference, which is a derivative-free adaptation of the Filter-SQP method, originally proposed by Fletcher and Leyffer [10], and to those obtained with the software COBYLA by Powell [25], a trust-region method for constrained problems that models the objective and constraint functions by linear interpolation.
Category: