A = [1 2 3;5 3 7; 4 7 8];
b = 39;66;17]
??? b = 39;66;17]
                |
{Error: Unbalanced or unexpected parenthesis or bracket.
} 
b = [39;66;17]
b =
    39
    66
    17
x = A\b
x =
          -28
        -29.8
         42.2
e = A*x-b
e =
     0
     0
     0
realmin
ans =
  2.2251e-308
formt long
{??? Undefined function or method 'formt' for input
arguments of type 'char'.
} 
format long
eps
ans =
    2.220446049250313e-016
1+eps
ans =
   1.000000000000000
x = 1+eps
x =
   1.000000000000000
x-1
ans =
    2.220446049250313e-016
eps2 = eps/2
eps2 =
    1.110223024625157e-016
x2 = 1 + eps2
x2 =
     1
x2-1
ans =
     0
A = rand(3)
A =
  Columns 1 through 2
   0.814723686393179   0.913375856139019
   0.905791937075619   0.632359246225410
   0.126986816293506   0.097540404999410
  Column 3
   0.278498218867048
   0.546881519204984
   0.957506835434298
formt short
{??? Undefined function or method 'formt' for input
arguments of type 'char'.
} 
format short
A
A =
    0.8147    0.9134    0.2785
    0.9058    0.6324    0.5469
    0.1270    0.0975    0.9575
b = rand(3,1)
b =
    0.9649
    0.1576
    0.9706
x = A\b
x =
   -2.5775
    3.0365
    1.0462
e = A*x-b
e =
  1.0e-015 *
   -0.4441
   -0.1110
    0.2220
v = [1 2 3]
v =
     1     2     3
v_sq = v.^2
v_sq =
     1     4     9
v_sum_sq = sum(v_sq)
v_sum_sq =
    14
v_mag = sqrt(v_sum_sq)
v_mag =
    3.7417
v_mag = sqrt(sum(v.^2))
v_mag =
    3.7417
v_mag = norm(v)
v_mag =
    3.7417
e
e =
  1.0e-015 *
   -0.4441
   -0.1110
    0.2220
norm(e)
ans =
  5.0877e-016
norm(e)/(1e6*eps)
ans =
  2.2913e-006