I see, so from an operation point of view, I should pass a 1D array... How should I unroll my nComp x nComp matrix? by row or by column? 

e.g. say that my block is:

A=[

      1 2 3 

      4 5 6

      7 8 9

     ]

than v = [1 2 3 4 5 6 7 8 9] or [1 4 7 2 5 8 3 6 9]?