javascript check radio buttons automatically

<input id="material_0" type="radio" name="material" value="30" >
<input id="material_1" type="radio" name="material" value="30" >



for (i=0; i<document.getElementsByTagName('input').length; i++)
 {
//if (document.getElementsByTagName('input')[i].type == 'radio')
var k=0;
var matId='material_'+i;

//document.getElementsByTagName('input')[i].id
                        //document.getElementsByTagName('input')[i].valau
if(document.getElementsByTagName('input')[i].name=='material')
{
var resetRadio=document.getElementsByTagName('input')[i].id;

document.getElementById(resetRadio).checked=false;

}
}