A(2,1)=4;
b=[3 ; 2; 9];
condA=cond(A)
relErrMatlab=eps(1)*condA
if relErrMatlab >= 0.1
    disp('There is no reasonable solution to this system!')
else
    x = A\b
    if relErrMatlab>0.001
        disp('Warning: the above solution may have noticeable error!')
    end
end
