N = size of sample set

O[N]     => linear
O[NlogN] => FFT
O[N**2]  => not so good
O[N**3]  => bad

=====
p01.exe 10 100 1000

int main(int argc, char** argv) {

  float joe[99][99];
  float* joe[99];

  

  char**** joe = 

  int nrows = atoi(argv[1]);

  // matrix multiply

  [1 2]  [6 7]  = [1*6 + 2*8  1*7 + 2*9] => 8 multiplies + 4 additions
  [3 4]  [8 9]    [3*6 + 4*8  3*7 + 4*9]

  [1 2 3 4]  [1 2]  = [4 mults + 3 additions ...] => (8x4 multiplies) = 32 multiplies
  [5 6 7 8]  [3 4]    [...]
             [5 6]
             [7 8]
    
  2x2 => 2x4: 8 => 32 multiplies, is this linear? quadratic with nrows?

Autocorrelation:

 R[k] = sum x[n]x[n+k]

 N = 3

 R[0] = x[0]*x[0] + x[1]*x[1] + x[2]*x[2] => 3 multiplies and 2 additions
 R[1] = x[0]*x[1] + x[1]*x[2] + x[2]*x[3] => 3 multiplies and 2 additions
 R[2] = ...

 for N data points and K lags: no. of multiplies => K*N multiplies








    
p01.exe 10 100 1000

int main(int argc, char** argv) {

  float joe[99][99];
  float* joe[99];

  

  char**** joe = 

  int nrows = atoi(argv[1]);

  // matrix multiply

  [1 2]  [6 7]  = [1*6 + 2*8  1*7 + 2*9] => 8 multiplies + 4 additions
  [3 4]  [8 9]    [3*6 + 4*8  3*7 + 4*9]

  [1 2 3 4]  [1 2]  = [4 mults + 3 additions ...] => (8x4 multiplies) = 32 multiplies
  [5 6 7 8]  [3 4]    [...]
             [5 6]
             [7 8]
    
  2x2 => 2x4: 8 => 32 multiplies, is this linear? quadratic with nrows?

Autocorrelation:

 R[k] = sum x[n]x[n+k]

 N = 3

 R[0] = x[0]*x[0] + x[1]*x[1] + x[2]*x[2] => 3 multiplies and 2 additions
 R[1] = x[0]*x[1] + x[1]*x[2] + x[2]*x[3] => 3 multiplies and 2 additions
 R[2] = ...

 for N data points and K lags: no. of multiplies => K*N multiplies