#500000		sparse				full			#50000		sparse				full
#nb threads	times		nb iter		times		nb iter			times		nb iter		times       nb iter		
1024		523		27 		2100.7		   					   		8.61	    16
512		449.426 	24		1459.35									9.27	    19
256             440.805 	24		754.24									7.73	    15
128		456.175 	22		718.623		27							8.64	    21
64		472.862 	23		715.554		27							7.84	    16
32		830.152		24		1089.61		27							11.33	    18
16		1234		24		1746.53		22							20.47	    21
8		2632.78		23 		3112		20							35.07	    26