I want to add new columns by clicking a button in jqGrid.

Question

I want to add new column on a button click in jqGrid. Following is the code that i am using to define a grid. can someone help me, how to define new columns with position.

 jQuery("#list").jqGrid({ 
  datatype: "local", 
  height: 250, 
  colNames:['Inv No','Date', 'Client', 'Amount','Tax','Total','Notes'], 
  colModel:[ 
      {name:'id',index:'id', width:60, sorttype:"int",editable:false,editoptions:{readonly:true,size:10}}, 
      {name:'invdate',index:'invdate', width:90, sorttype:"date",editable:true,editoptions:{readonly:false,size:25}}, 
      {name:'name',index:'name', width:100, editable:true,editoptions:{readonly:false,size:20}},
      {name:'amount',index:'amount', width:80, align:"right",sorttype:"float", editable:true, editoptions:{readonly:false,size:20}}, 
      {name:'tax',index:'tax', width:80, align:"right",sorttype:"float", editable:true,editoptions:{readonly:false,size:20}}, 
      {name:'total',index:'total', width:80,align:"right",sorttype:"float", editable:true,editoptions:{readonly:false,size:20}}, 
      {name:'note',index:'note', width:150, sortable:false, editable:true,editoptions:{readonly:false,size:20}} 
      ],
  rowNum:10,
  rowList:[10,20,30],
  sortname: 'id',
  viewrecords: true,
  sortorder: "desc",
  editCaption: "Edit Record",
  caption: "Manipulating Grid Data",
  editurl:"someurl.php"
 });