Math calculations

Calculate sum of children values automaticaly with [=sum]
Source
    
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<script  src="../../../dhtmlxGrid/codebase/dhtmlxgrid.js"></script>
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<script  src="../../codebase/dhtmlxtreegrid.js"></script>
<script  src="../../../dhtmlxGrid/codebase/ext/dhtmlxgrid_math.js"></script>
            <div id="gridbox" width="519px" height="220px" style="background-color:white;"></div>
<br>
 
<script>mygrid = new dhtmlXGridObject('gridbox');
mygrid.imgURL = "../../../dhtmlxGrid/codebase/imgs/icons_books/";
mygrid.setHeader("Title,Price,Quantity,Total");
mygrid.setInitWidths("*,70,120,120");
mygrid.setColAlign("left,right,right,right");
mygrid.setColTypes("tree,price,ed[=sum],price[=sum]");
mygrid.setColSorting("str,int,int,int");
mygrid.setMathRound(2);
mygrid.init();
mygrid.setSkin("dhx_skyblue");
mygrid.loadXML("../common/grid_math3.xml");</script>