function auto_height(){
////////////最大值
var max;

if(typeof(left) != "undefined")
max=left.scrollHeight;

if(typeof(middle) != "undefined"){
if(middle.scrollHeight>max)
max=middle.scrollHeight;
}
 
if(typeof(right) != "undefined"){
if(right.scrollHeight>max)
max=right.scrollHeight;
}
///////////自动定位层
if(typeof(left) != "undefined"){
if(left.scrollHeight<max)
document.all.left.style.height=max;
}

if(typeof(middle) != "undefined"){
if(middle.scrollHeight<max)
document.all.middle.style.height=max;
}

if(typeof(right) != "undefined"){
if(right.scrollHeight<max)
document.all.right.style.height=max;
}

if(typeof(bottom) != "undefined"){
if(bottom.scrollHeight<max)
document.all.bottom.style.top=max+head.scrollHeight;
}
/////////end
}