>> h_x = [1/3 1/3 1/3]

h_x =

    0.3333    0.3333    0.3333

>> h1 = conv(h_x, h_x)

h1 =

    0.1111    0.2222    0.3333    0.2222    0.1111

>> h2 = conv(h1, h_x)

h2 =

    0.0370    0.1111    0.2222    0.2593    0.2222    0.1111    0.0370

>> h3 = conv(h2, h_x)

h3 =

    0.0123    0.0494    0.1235    0.1975    0.2346    0.1975    0.1235    0.0494    0.0123

>> h4 = conv(h3, h_x)

h4 =

    0.0041    0.0206    0.0617    0.1235    0.1852    0.2099    0.1852    0.1235    0.0617    0.0206    0.0041

>> plot(h1)
>> plot(h2)
>> plot(h3)
>> plot(h4)
>> h5 = conv(h4, h_x)

h5 =

  Columns 1 through 11

    0.0014    0.0082    0.0288    0.0686    0.1235    0.1728    0.1934    0.1728    0.1235    0.0686    0.0288

  Columns 12 through 13

    0.0082    0.0014

>> h6 = conv(h5, h_x);
>> h7 = conv(h6, h_x);
>> h9 = conv(h8, h_x);
??? Undefined function or variable 'h8'.

>> h8 = conv(h7, h_x);
>> h9 = conv(h8, h_x);
>> plot(h9)