 However, most model learning methods developed within adaptive nonlinear control are limited to certain types of uncertainties, called matched uncertainties  .
<meaning-changed>  However, most model learning methods developed within adaptive nonlinear control are limited to certain types of uncertainties, called matched uncertainties  .
 However, most model learning methods developed within adaptive nonlinear control are limited to certain types of uncertainties, called matched uncertainties , because the certainty equivalency principle can be employed in the design phase .