Linear Fractional Transformation Identification Using Retrospective Cost Optimization

In this paper we use retrospective cost optimization to identify linear fractional transformations (LFTs). This method uses an adaptive controller in feedback with a known system model. The goal is to identify the feedback portion of the LFT by adapting the controller with a retrospective cost. We demonstrate this method on numerical examples of increasing complexity, ranging from linear examples with unknown feedback terms to nonlinear examples. Finally, we examine methods for improving the retrospective cost optimization performance.