disp('question 2)a)')      //exemples de R. S. Wilson
A=[10 7  8  7 ;
    7 5  6  5 ;
    8 6 10  9 ;
    7 5  9 10 ];
B=[32 23 33 31]';
deltaA=[ 0     0     0.1  0.2  ;
         0.08  0.04  0    0    ;
         0    -0.02 -0.11 0    ;
        -0.01 -0.01  0   -0.02 ];
deltaB=[0.1 -0.1 0.1 -0.1]';
spectreA=spec(A);
printf(' \nLes valeurs propres de A sont :\n..
lambda1 = %.2f, lambda2 = %.2f, lambda3 = %.2f et lambda4 = %.2f\n ',..
spectreA(1),spectreA(2),spectreA(3),spectreA(4))
condA=cond(A)
condAbis=max(abs(spectreA))/min(abs(spectreA))

disp('question 2)b)')
X=A\B
Xbis=A\(B+deltaB)
Xter=(A+deltaA)\B

disp('question 2)c)')
quotient1=norm(Xbis-X)/norm(X)
majorant1=condA*(norm(deltaB)/norm(B))
quotient2=norm(Xter-X)/norm(Xter)
majorant2=condA*(norm(deltaA)/norm(A))