angularjs switch tab view using ui.bootstrap

Question

I have set up two buttons to switch to other two tabs on click, but it is not working.

here is the html code:

<div ng-controller="TabCtrl">
    <uib-tabset class="tabbable">
        <uib-tab heading="my tab 0" ng-attr-active="tabs[0].active">
            <div class="row">

            <a class="btn btn-wide btn-azure" ng-click="go_tab1()">
            Go To tab 1
            </a>
            <a class="btn btn-wide btn-azure" ng-click="go_tab2()">
            Go To tab 2
            </a>
            </div>
        </uib-tab>
        <uib-tab heading="my tab 1" ng-attr-active="tabs[1].active">
            <div class="row">
            </div>
        </uib-tab>
        <uib-tab heading="my tab 2" ng-attr-active="tabs[2].active">
            <div class="row">
            </div>
        </uib-tab>
    </uib-tabset>
</div>

here is the controller:

$scope.tabs = [{active: true}, {active: false}, {active: false}];
$scope.go_tab1 = function() {
    $scope.tabs[1].active = true;
};
$scope.go_tab2 = function() {
    $scope.tabs[2].active = true;
};