0x0 matrix
triplet:
( )
( )
( )
compressed:
( )
( )
( 0 )

3x3 matrix
triplet:
( 100 0 100 1 100 2 100 6 100 7 100 8 )
( 0 0 0 0 0 0 2 2 2 2 2 2 )
( 0 0 1 1 2 2 0 0 1 1 2 2 )
compressed:
( 100 0 100 6 100 1 100 7 100 2 100 8 )
( 0 0 2 2 0 0 2 2 0 0 2 2 )
( 0 4 8 12 )