clear all

A = [ 81 -54 -63   0   0   0 ;
     -54 180 102  24   0   0 ;
     -63 102 138 -14  24   0 ;
       0  24 -14  14 -13  -9 ;
       0   0  24 -13  61  30 ;
       0   0   0  -9  30 182 ] ;

b = [36 ; 276 ; -87 ; 85 ; -35 ; 823] ;

x = bicg     (A , b) % Biconjugate gradient
x = bicgstab (A , b) % Biconjugate gradient stabilized
x = cgs      (A , b) % Conjugate gradient squared
x = gmres    (A , b) % Generalized minimum residual
x = lsqr     (A , b) % LSQR (Conjugate Gradients on the Normal Equations)
x = minres   (A , b) % Minimum residual
x = pcg      (A , b) % Preconditioned conjugate gradient
x = qmr      (A , b) % Quasiminimal residual
x = symmlq   (A , b) % Symmetric LQ