Formula not working set colmodel after grid initialization

[Kayser]

Hi everyone,
New colmodel option "formula" not working after grid initialization. When I set colmodel dynamically,  any column's formula option can't load.

Example:
var obj = {colModel:[{title:"#"}]};

$("selector").pqGrid(obj);

Actually  bottom colModel comes from an ajax response;

var colModel = [{title:"1.Column",dataIndx:1, dataType:"integer" }, {title:"2.column", dataIndx:2, dataType:"integer", formula: function(ui) {return ui.rowData[1]*10;}}]

$("selector").pqGrid("option","colModel", colModel); // <= In here formula not load

I have to set colModel like this . Do you have any idea?

Thanks in advance.