Dynamic Creation in WD

Dear Team,

I want to create Dynamic Group in Web Dynpro under ROOTUIELEMENTCONTAINER.

Below is the code i have written.

  root ?= view->get_element('ROOTUIELEMENTCONTAINER').

cl_wd_matrix_layout=>new_matrix_layout( root ) .

    cl_wd_group=>new_group(

     EXPORTING

         id                       = 'G1'

         view                     = view

     RECEIVING

          control                 = lr_group ).

     root->add_child( lr_group ).

     lr_matrix =  cl_wd_matrix_layout=>new_matrix_layout( lr_group ).

If i commented below line i got exception.

        cl_wd_matrix_layout=>new_matrix_layout( root ) .

So my question is it mandatory to set the matrix layout of the parent element, in my case parent element it is 'ROOTUIELEMENTCONTAINER'.

Because in my case i have used the flow layout attribute under ROOTUIELEMENTCONTAINER.

Manually it's possible but dynamically its not possible.

Thanks

Nishant