angularjs – 我怎样才能默认使用手风琴来打开第一个元素？

这是工作fiddler.

这是HTML代码：

<div ng-app="myapp">
  <div ng-controller="AccordionDemoCtrl">
    <uib-accordion close-others="oneAtATime">
      <uib-accordion-group ng-repeat="group in groups" is-open="isOpen">
                      <uib-accordion-heading>
                    <div class="text-center">
                        <strong>{{group.title}}</strong>
                        <i class="pull-right glyphicon" ng-class="{'glyphicon-chevron-down': isOpen,'glyphicon-chevron-right': !isOpen}"></i>
                    </div>
                </uib-accordion-heading>
      {{group.content}}</uib-accordion-group>
    </uib-accordion>
  </div>
</div>

这是控制器：

var app = angular.module('myapp',['ui.bootstrap','ngAnimate'])

app.controller('AccordionDemoCtrl',function($scope) {
  $scope.groups = [{
    title: "Dynamic Group Header - 1",content: "Dynamic Group Body - 1"
  },{
    title: "Dynamic Group Header - 2",content: "Dynamic Group Body - 2"
  },{
    title: "Dynamic Group Header - 3",content: "Dynamic Group Body - 3"
  }];
});

我试着用这一行：

is-open="true"

像那样：

<uib-accordion-group heading="{{group.title}}" ng-repeat="group in groups"  is-open="true">{{group.content}}</uib-accordion-group>

但它默认打开所有项目.

我怎么能默认使用手风琴才能打开第一个元素？

附：这是更新plunker