isSelected = false;

function matSelect() {
  var items = matSelect.arguments.length

    for (i = 0; i < document.search_doc.length; i++)
         for (j = 0; j < items; j++)
      if (document.search_doc.elements[i].value == matSelect.arguments[j]) {
         if ( document.search_doc.elements[i].checked == false){
          document.search_doc.elements[i].checked = true ;
         }
         else{
          document.search_doc.elements[i].checked = false ;
         }
}
     isSelected = true;
     return isSelected;
}