def execute(self):

        bracket_invalid = self._eval(self.lower_bound)*self._eval(self.upper_bound) > 0

        # check if user supplied function to handle resizing bracket
        if bracket_invalid and self.f_resize_bracket:

            # try to resize bracket to find a valid bracket.
            iteration = 1
            should_continue = True
            bracket_invalid = True

            while bracket_invalid and should_continue:
                self.lower_bound, self.upper_bound, should_continue = \
                    self.f_resize_bracket(self.lower_bound, self.upper_bound, iteration)

                bracket_invalid = self._eval(self.lower_bound)*self._eval(self.upper_bound) > 0
                iteration += 1

        if bracket_invalid:  # if bracket is still invalid, see if user has specified what to return

            if self.invalid_bracket_return >= 0.0 and 1.0 <= self.invalid_bracket_return:
                xstar = self.lower_bound + self.invalid_bracket_return*(self.upper_bound-self.lower_bound)
                brent_iterations = 'valid bracket not found.  returning user specified value'

            else:
                self.raise_exception('bounds (low=%s, high=%s) do not bracket a root' %
                                 (self.lower_bound, self.upper_bound))

        else:

            kwargs = {'maxiter': self.maxiter, 'a': self.lower_bound,
                      'b': self.upper_bound, 'full_output': True}

            if self.xtol > 0:
                kwargs['xtol'] = self.xtol
            if self.rtol > 0:
                kwargs['rtol'] = self.rtol

            # Brent's method
            xstar, r = brentq(self._eval, **kwargs)
            brent_iterations = r.iterations


        # Propagate solution back into the model
        self.set_parameters([xstar])
        self.run_iteration()
  
        if self.iprint == 1:
            print 'iterations:', brent_iterations
            print 'residual:', self.eval_eq_constraints()
dataset/ETHPy150Open OpenMDAO/OpenMDAO-Framework/openmdao.lib/src/openmdao/lib/drivers/brent.py/Brent.execute/swapped operands of `<=`