function all_rows = AddRowsWithZeroPadding( start_rows, add_rows )

start_width = size( start_rows, 2 );
add_width = size( add_rows, 2 );
new_width = max( start_width, add_width );

all_rows = [ start_rows, zeros( size( start_rows, 1 ), new_width - start_width )
             add_rows, zeros( size( add_rows, 1 ), new_width - add_width ) ];