code: func (r Virtual_PlacementGroup) GetAvailableRouters(datacenterId *int) (resp []datatypes.Hardware, err error) {
  	params := []interface{}{
  		datacenterId,
  	}
  	err = r.Session.DoRequest("SoftLayer_Virtual_PlacementGroup", "getAvailableRouters", params, &r.Options, &resp)
  	return
  }
docs: // Returns all routers available for use with placement groups. If a datacenter location ID is provided, this method will further restrict the list of routers to ones contained within that datacenter.