Need a matlab code for creating COVARIANCE matrix

I have a matrix size - (1024rows x 3 columns). I need to create such a code that it will calculate covariance matrix for first 4 rows...i.e. rows (1to 4) then (5 to8) then row (9-12) then (13-16) and continue till ...rows(1020 to 1024. I am mentioning my first 4 rows here e.g.

    8.3000   74.7000    0.1080
A=  8.2000   74.9000    0.1080
    8.2000   73.7000    0.1080
    8.7000   72.9000    0.0450

calculated manually-

cov (A) =

    0.0567   -0.1700   -0.0073
   -0.1700    0.8633    0.0241
   -0.0073    0.0241    0.0010

code should work till calculates cov matrix for last rows (1020 to 1024).