ACOVF estimates autocovariance function (not normalized)
 NaN's are interpreted as missing values. 

 [ACF,NN] = acovf(Z,MAXLAG,Mode);

 Input:
  Z    Signal (one channel per row);
  MAXLAG  maximum lag
  Mode	'biased'  : normalizes with N [default]
	'unbiased': normalizes with N-lag
	'coeff'	  : normalizes such that lag 0 is 1	
        others	  : no normalization

 Output:
  ACF autocovariance function
  NN  number of valid elements 

 REFERENCES:
  A.V. Oppenheim and R.W. Schafer, Digital Signal Processing, Prentice-Hall, 1975.
  S. Haykin "Adaptive Filter Theory" 3ed. Prentice Hall, 1996.
  M.B. Priestley "Spectral Analysis and Time Series" Academic Press, 1981. 
  W.S. Wei "Time Series Analysis" Addison Wesley, 1990.
  J.S. Bendat and A.G.Persol "Random Data: Analysis and Measurement procedures", Wiley, 1986.

Package: tsa