-------------------------------------------------
a)
-------------------------------------------------
A =

   1.0000   2.0000
   1.0010   2.0000

cond_A =  6002.0
rel_error =  2
relative_residual =  6.6644e-04
error_bound =  4
-------------------------------------------------
b)
-------------------------------------------------
A =

   2.0100   1.9900
   1.9900   2.0100

cond_A =  200.00
rel_error =  1
relative_residual =  0.0050000
error_bound =  1.0000
-------------------------------------------------
c)
-------------------------------------------------
A =

   1  -1  -1
   0   1  -1
   0   0   1

cond_A =  12
rel_error =  0.050000
relative_residual =  0.10000
error_bound =  1.2000
-------------------------------------------------
d)
-------------------------------------------------
A =

   1.00000   0.50000   0.33333
   0.50000   0.33333   0.25000
   0.33333   0.25000   0.20000

cond_A =  748.00
rel_error =  0.020000
relative_residual =  0.020000
error_bound =  14.960