>> n=0:20;
>> h=0.8.^n;
>> x=ones(1,5);
>> y=conv(h,x);
>> stem(y)
y =

  Columns 1 through 6 

    1.0000    1.8000    2.4400    2.9520    3.3616    2.6893

  Columns 7 through 12 

    2.1514    1.7211    1.3769    1.1015    0.8812    0.7050

  Columns 13 through 18 

    0.5640    0.4512    0.3609    0.2888    0.2310    0.1848

  Columns 19 through 24 

    0.1478    0.1183    0.0946    0.0665    0.0440    0.0259

  Column 25 

    0.0115
>> title('the second 卷積');
>> xlabel('n');
>> ylabel('y');