Adding a header cell to a matrix model

Hi,
I've tried some things to add header cells to a matrix model, but I don't khow we is the problem: after execution there is no cells added !!
I think the code is right, can any body help ?

var nLocale = Context.getSelectedLanguage();
var groups = ArisData.getSelectedGroups();
var group = groups[ 0 ];

var modelMatrice = group.CreateModel( 220 , "A vs B" , nLocale );
var matrix = modelMatrice.getMatrixModel();

var matrixRowHeader = matrix.getHeader( true );
var matrixColHeader = matrix.getHeader( false );

matrixRowHeader.setTitle( group.Name( nLocale ) , nLocale );

var objectGroupInRows = group.ObjDefList();
var matrixHeaderCell = null;;
for (var i=0;i