% @(#)covar_tsa.hlq	19.1 (ESO-IPG) 02/25/03 13:32:44
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%.COPYRIGHT (c) 1992 European Southern Observatory & Copernicus Astron. Center%.IDENT     covar_tsa.hlq
%.AUTHOR    Alex Schwarzenberg-Czerny, ESO & Copernicus Astronomical Center 
%.KEYWORD   MIDAS, help files, COVAR/TSA
%.LANGUAGE  LATEX
%.PURPOSE   Compute discrete covariance function for unevenly sampled data
%.VERSION   0.0               June 1992
%.RETURNS   None  
%.ENVIRON   TSA context
%-----------------------------------------------------------------------------
\se
SECTION./TSA
\es\co
COVAR/TSA                               15-SEPT-1992 A.Schwarzenberg-Czerny
\oc\su
COVAR/TSA intab1 intab2 outtab start step nsteps scale
	compute discrete covariance function for unevenly sampled data
\us\pu
Purpose: 
          Compute discrete covariance function for unevenly sampled data.
          The binned covariance function is returned with its errors.
          For reference see Ap.J. 333, 646.
\up\sy
Syntax:
          COVAR/TSA intab1 intab2 outtab start step nsteps [scale] [funct]
\ys\pa
          intab1 = name of the table containing 1st set of observations with 
                   their variances. The table must contain columns :TIME :VALUE 
                   and :VAR in DOUBLE PRECISION. For numerical reasons it is 
                   advisable to subtract mean from :VALUE.
\ap\pa
          intab2 = same for 2nd time series.
\ap\pa
          outtab = name of the output table containing the covariance 
                   function. 
\ap\pa
          start  = start value of time lag in the output table, in units
                   of time or log time depending on value set for the parameter 
                   scale. 
\ap\pa
          step   = step of time lags in the table, in units of time or log 
                   time depending on value set for the parameter scale. 
\ap\pa
          nsteps = number of time lags in the table
\ap\pa
          scale  = type of lag scale to be used (LINear or LOGarithmic). 
                   The default value is LIN.
\ap\pa
          funct  = type of output function:
               C - correlation function (default), C(lag)= <x(t)*y(t+lag)>
               S - structure function,   S(lag)= <(x(t)-y(t+lag))**2>/2, \\
              where C(lag)=sqrt(Var[x]*Var[y])-S(lag), Var[] is signal variance
              and is assumed that both signals have null mean.
\ap\sa
See also:
          SHOW/TSA, DELAY/TSA
\as\no
Note:
          This command can be used for the calculation of the autocovariance
          function.
\on\exs
Examples:
\ex
          COVAR/TSA DATA1 DATA2 COV 1. 0.1 31
\xe\ex
          COVAR/TSA DATA1 DATA1 AUTOCOV 
          returns the autocovariance function if time lag grid was defined by a           previous call 
\xe\sxe
