function autosize(){
	var col1 = document.getElementById('col1');
	var col2 = document.getElementById('col2');
	var col3 = document.getElementById('col3');
	// grootste bepalen
	var _newHeight = col1.offsetHeight;
	if(col2.offsetHeight > _newHeight){
		_newHeight = col2.offsetHeight;
	}
	if(col3.offsetHeight > _newHeight){
		_newHeight = col3.offsetHeight;
	}
	col1.style.height=_newHeight +'px';
	col2.style.height=_newHeight +'px';
	col3.style.height=_newHeight +'px';

} // function autosize