function show_matrix (tohighlight,col) 
{
        var tohighlight = tohighlight.split(",");
	var tag=document.getElementsByTagName("p");//all p-tags
        for(i=0;i<tag.length;i++) 
	{    
            var str=tag[i].id.charAt(0);            
            if(str != col)
	    {
            	tag[i].className="matrix_bg";
            }
        }
	
	for (var i=0; i < tohighlight.length; ++i) 
	{
		document.getElementById(tohighlight[i]).className="matrix_on";
	}
		
}

		
function hide_matrix () 
{
    tag=document.getElementsByTagName("p");
    for(i=0;i<tag.length;i++) 
    {
        if(tag[i].id)
	{
        	tag[i].className="matrix_off";
        }
    }

}