double LogisticRegression<MatType>::ComputeError(
    const MatType& predictors,
    const arma::Row<size_t>& responses) const
{
  // Construct a new error function.
  LogisticRegressionFunction<> newErrorFunction(predictors, responses,
      lambda);

  return newErrorFunction.Evaluate(parameters);
}
double LogisticRegression<OptimizerType>::ComputeError(
    const arma::mat& predictors,
    const arma::vec& responses) const
{
  // Construct a new error function.
  LogisticRegressionFunction newErrorFunction(predictors, responses,
      lambda);

  return newErrorFunction.Evaluate(parameters);
}