result4 = [16, -120, 240, -140;
	   -120, 1200, -2700, 1680;
	   240, -2700, 6480, -4200;
	   -140, 1680, -4200, 2800];

(invhilb (1) == 1 && invhilb (2) == [4, -6; -6, 12]
 && invhilb (4) == result4
 && abs (invhilb (7) * hilb (7) - eye (7)) < sqrt (eps))
