#500000		sparse				full			#50000		sparse				full
#nb threads	times		nb iter		times		nb iter			times		nb iter		times       nb iter		
1024		523		27 		545		   					   		8.61	    16
512		449.426 	24		520									9.27	    19
256             440.805 	24		480									7.73	    15
128		456.175 	22		560									8.64	    21
64		472.862 	23		603									7.84	    16
32		830.152		24		920									11.33	    18
16		1234		24		1870									20.47	    21
8		2632.78		23 		3589									35.07	    26