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When the correct solution to registration was known, it was intriguing to see how the function would behave near that solution. Ideally, it should return to that correct solution quickly and quite controllably (in the sense that no abrupt data changes occur in the process). Two types of perturbations were attempted: random noise and a randomly-placed CPS warp. Results showed that the objective function failed to revert the data to its form in the correct solution. In fact, the objective function value dropped below that which was expected. This instability of the objective function is explained later in this subsection.