Xronos
CROSSCOR (Jan96)              xanadu.xronos             CROSSCOR (Jan96)



NAME
    crosscor  -- Calculates cross  correlation  using  a  fast  or  slow
    algorithm for 2 input time series
    
    
USAGE
    crosscor  file(s)+options  window  dtnb  nbint  nintfm  plot plotdev
    outfile
    
    
DESCRIPTION
    This task calculates the cross correlation of 2 input  time  series,
    plots   and  outputs  the  results  (in  a  FITS  file).  The  cross 
    correlation is computed either by an FFT algorithm or a direct  slow
    algorithm.  The  paramater  "fast" can be used to select the type of
    algorithm (the default is set to fast). The  input  file  format  is
    FITS  using  the  BINTABLE  extension.  Both  binned data format and
    event format are input.  It requires  two  simultaneous  input  time
    series   (See  FILELIST  and  INPUT  FILE  OPTIONS).   Time,  Phase, 
    Intensity  and  Exposure  windows  (See  WINDOW)  allow   for   data 
    screening.   Input  data  can be rebinned and divided into Intervals
    and Frames (See GENERAL XRONOS  TERMINOLOGY).  The  results  of  the
    cross  correlation  from  several  intervals  can  be  averaged in a
    frame. The standard plot output is  cross  correlation  versus  time
    delay  (see  PLOT).  The  time  delays  refer  to  the  1st  series: 
    therefore a cross correlation function  peaking  for  positive  time
    delays  indicates that variations in the 2nd series lag those in the
    1st series.  The cross correlation error bars are from the  standard
    deviation  of  the  average  of the cross correlations in each delay
    bin from different intervals, if the specified number  of  intervals
    per  frame  is  larger  than  the  value  of  "errorbars"  parameter 
    (default =5); otherwise error bars  are  set  =0.   For  the  "slow"
    method  only,  error  bars  are  also  obtained  by  propagating the
    theoretical error bars of the  cross  correlations  from  individual
    intervals  (in  turn  obtained by propagating the newbin errors bars
    through the cross  correlation  formula).  Different  normalizations
    can  be  used  for  the  auto  correlation by changing the parameter
    "normalization" (See normalization).
    
    
normalization
    The  "normalization"  paramater  has  the  following  meanings  (and 
    values) :
     * =0  cross correlations are normalised by dividing by the square root of the
           product of the number of good newbins of the two series in each 
           interval, i.e. they are cross covariances.
     * =1  (d/f); cross correlations are normalised as in the case =0 and by 
           dividing also by the square root of the product of the newbin variances 
           of the two series in each interval. 
     * =2  cross correlations are normalized as in the case =0 and by dividing 
           also by the square root of the product of the newbin excess variances 
           of the two series in each interval. Problems arise when, due to statistical 
           fluctuations, the excess variance of an interval is negative for any 
           of the two series. To avoid negative normalization, `crosscor` adopts 
           automatically normalization 1.
     * =3  cross correlations are normalized by dividing by the square root of the 
           product of the average newbin excess variances of the two series in each 
           frame after averaging the cross covariances. If the excess variance 
           in a frame is negative, for any of the two series, 'crosscor' 
           adopts automatically normalization 1. 
    If  other  values than those listed above are used, they are treated
    as =0.
    
    
GENERAL XRONOS TERMINOLOGY
    Within XRONOS tasks, BINS and NEWBINS control the  binning  used  in
    the  analysis,  INTERVALS  the  subdivision  of  the time series and
    FRAME the grouping of the output results:
    
    BINS : these are the time bins of the time  series  being  analysed.
    More  than one input file can have different bin durations, e.g. two
    consecutive time series, one with 0.5 s bins and the other with 2  s
    bins.  The  original  bin time is the value stored in the input file
    in the keyword TIMEDEL. If the data are stored in  each  row  as  an
    array  with  1CTYPn  =  'TIME', the original bin is set to the value
    stored in the keyword 1CDLTn (where n is the column number).
    
    NEWBINS : these correspond to  the  time  resolution  at  which  the
    analysis  is  carried out.  Note that: (i) newbins cannot be shorter
    than the longest bin duration of the  time  series  being  analysed;
    (ii)  in many XRONOS applications (e.g. powspec, autocor, crosscorr)
    the newbin duration is forced to  be  an  integer  multiple  of  the
    longest bin duration.
    
    INTERVAL  :  an  interval  is  defined by the number of newbins over
    which the analysis is carried out. Note that in  applications  using
    FFT  algorithms  (e.g.  powspec,  autocor  and  crosscor set in fast
    mode) the number of newbins in an interval is a power of 2.
    
    FRAME : a frame consists of  the  average  of  the  results  of  the
    analysis   of  one  or  more  contiguous  intervals.  Note  that  in 
    'lcurve', 'efsearch' and 'lcstats' a frame consists  always  of  one
    interval.
    
    
WINDOWS 
    If  any  window  is  required  during  the  analysis,  a window file
    containing  the  relevant  windows  must   be   created   with   the 
    application  XRONWIN,  before  running  a  XRONOS task.  There are 4
    different types of windows :
     * Time Windows  : consist of up to 1000 time intervals                  
     * Phase Windows : consist of an Epoch, a Period and up to 10 phase intervals
     * Intensity Windows : consist of up to 10 intensity in bin, newbin and interval
     * Exposure Windows : consist of up to 1 exposure in bin, newbin and interval 
    Intensity and Exposure Windows can be specified  independently  for:
    (i)  Bins  , (ii) New Bins , (iii) Intervals. When dealing with more
    than one  time  series,  Intensity  and  Exposure  Windows  must  be
    specified  separately  for  each series.  Time and Phase windows are
    applied to Bins. Intensity and Exposure windows  are  applied  first
    to  Bins,  then  Newbins and finally to Intervals as specified.  For
    time and phase windows, only those bins whose center time is  within
    the  start  and  stop  of  a  time  window  or  phase  window (for a
    specified epoch and period) are accepted. Intensity windows must  be
    ordered  with  increasing  intensity  and  if set for newbins can be
    used in conjunction  with  "Special  Newbin  Windows"  (see  below).
    Exposure  Windows consist of a minimum and a maximum exposure level.
    Units are such that 1 means 100% exposure. The  Newbin  Exposure  is
    obtained  by  propagating  the  bin  exposures  to  each newbin. For
    example, if in a 30 s newbin the total exposure (due to the  sum  of
    the  individual  exposure  of  the  bins  contributing  to the given
    newbin) is 18 s then its exposure is 60%. The Interval  Exposure  is
    the  ratio  of  accepted  to expected newbins: for example, if a 128
    newbin long interval contains only 32  accepted  newbins,  then  its
    exposure  is  25%. Many XRONOS application use some default exposure
    windows, which are designed to avoid analysing data sets  which  are
    too  inhomogeneous with respect to their statistical properties. The
    minimum default Exposure windows in an Interval is  set  to  0.0  in
    the  lcurve,  efold  and efsearch and to 0.5 (i.e. 50% exposure ) in
    all the other tasks. Note that exposures can  be  higher  than  100%
    (e.g.  if  the  newbin  time is not a multiple of the bin time, then
    "beats" are generated which might bring the exposure of a newbin  to
    values  >100%;  or  if  two  or  more  input files for the same time
    series overlap in part, some of the newbins will be more  than  100%
    exposed).   IMPORTANT  NOTE  WHEN TIME WINDOWS ARE SET IN THE WINDOW
    FILE: The time used within XRONOS tasks  is  Truncated  Julian  Days
    (TJD=  JD-2440000.5)  if either (1) the keyword MJDREF is present in
    the header or (2) if the TIMESYS  value  is  one  of  the  following
    strings  MJD  or JD or TJD.  If (2), the time values are expected to
    be stored as JD, MJD or TJD in the header keywords and in  the  TIME
    column  in  which case the MJDREF keyword is not used (it should not
    be present). When Time windows are set using XRONWIN, they  must  be
    compatible  with  the values in header of the timing keywords and/or
    the values in the TIME column.
    
    An additional window type called "Special Newbin Window" can be  set
    directly  from  the  parameter file. Special Newbin Windows are used
    to exclude the parts of a light curve which  immediately  follow  or
    precede  a  burst  or  a background event which has been rejected by
    intensity  windows  in  newbins.  The  Special  Window  operates  on 
    newbins  in  conjunction with intensity windows (in newbins) and are
    specified  by   changing   to   positive   values   the   parameters 
    'spwinbefore'  and  'spwindowafter'.  Their use is the following: if
    e.g. spwinbefore is set =10,  all  newbins,  whose  center  time  is
    within  10  second  before  the  center time of a newbin rejected by
    intensity windows, will also be rejected; if e.g.  spwindowafter  is
    set  =20,  all  newbins, whose center time is within 20 second after
    the center time of a newbin  rejected  by  intensity  windows,  will
    also be rejected.
    
    
FILELIST and INPUT FILE OPTIONS
    To  input multiple files for each time series, a file containing the
    list of files is needed (Filelist). The Filelist  is  input  in  the
    program  as  '@Filelist'.  The format of this file list is ascii and
    contains one filename+options per line. Files from  different  times
    series  are  separated  by  '///'  mark.  Below is an example of the
    Filelist containing 2 files for 3 different times series.
     file1_ser1
     file2_ser1
     ///
     file1_ser2
     file2_ser2
     ///
     file1_ser3
     file2_ser3
    The Input File Options (up to 10) can be specified for each file  in
    the  same  input string.  They consist of 2 characters followed by a
    numerical constant (up to 8 character long).  There are  two  groups
    of   options.   The  first  allows  data  selection  within  a  FITS 
    extension. The available options within this group are :
     frN= start reading input file from row number N (first row)
     lrN= stop reading input file from row number N (last row) 
     vxN= use column number N as x-axis (i.e. time axis, default name is TIME)
     vyN= use column number N as y-axis (default names are COUNT or RATE)
     vsN= use column number N as error for y-axis (default name is ERROR)
     veN= use column number N as exposure (default name FRACEXP).
          If the input file is an event list, exposure is by default
          calculated using the GTI extension. In this case, N=0
          turns off the usage of the GTI extension for the exposure
          calculation, and N > 0 specifies the GTI extension to use.
     feN= select data (either binned or events) from channel number N (First Energy). 
          For an event list channel selection is made using the column named 'PHA'
     leN= select data (either binned or events) to channel number N (Last Energy). 
          For event list the default column channel name searched is 'PHA'.
          The option 'vcN' allows the choice of a channel column name different from 'PHA' (es. 'PI').
     vcN= use column number N for channel selection (valid only for event lists). 
     rtN= use extension N of the FITS file to read the data. The first extension 
          is N=1 (the primary array is irrelevant). To specify the extension the 
          following also can be used: filename[N] or filename+N.  
     of = The MJDREF keyword is not used. The time is calculated using the
          TIME column and the TIMEZERO keyword. 
    
    The  second  group  of  options  performs  algebraic  operations  on 
    individual  input  files.   They  are  applied  in the same order in
    which are specified. For event files  they  are  applied  after  the
    data are binned. The available options within this group are:
    
     stX = Shift all Time in input file by X days 
     ssX = Shift all times in input file by X Seconds 
     muX= multiply data and errors by X (MUltiply)
     mdX= multiply data by X (Multiply Data) 
     meX= multiply errors by X (Multiply Errors
     maX= as muX but exposure is divided by X 
     diX= divide data and errors by X (DIvide)
     ddX= divide data by X (Divide Data) 
     deX= divide errors by X (Divide Errors) 
     daX= as diX but exposure is multiplied by X
     aaX= add data and errors with X (Add All) 
     adX= add data with X (Add Data) 
     aeX= add errors with X (Add Errors) 
     saX= subtract data and errors with X (Subtract All)
     sdX= subtract data with X (Subtract Data) 
     seX= subtract errors with X (Subtract Errors) 
     qaX= add to data the square of data muliplied by X and add to errors 
          the product of data and error multiplied by X 
     qdX= as above but for data only
     qeX= as above but for error only 
    Below  is  an  example  of  the  Filelist  containing  2 files for 3
    different times series where the different options  are  applied  to
    the input files for different time series.
    
     file1_ser1 aa4           add to data and error 4 
     file2_ser1 aa4            "      "        "    "
     ///
     file1_ser2 rt2 aa2       read 2nd extension; add to data and error 2 
     file2_ser2 rt2 aa2        "    "     "           "      "        "    "   
     ///
     file1_ser3 rt2 vy4 vs5   read 2nd extension; use column 4 and 5 for Y-axis and Error
     file2_ser3 rt2 vy4 vs5    "    "    "         "    "    "     "  "   "          " 
    
    
    
PLOT
    The  array  of results from each XRONOS task can be plotted. The PLT
    routine (See also QDP/PLT manual) provides the interactive  plotting
    and  fitting  functions.  The plotting function is available for the
    following  tasks  :  autocor,  crosscor,  efold,  efsearch,  lcurve, 
    powspec  and timeskew. The 'crossocor' plot is the cross correlation
    function versus time delay (positive and negative) given in seconds.
    A  number of commands can be entered from the 'PLT>' prompt to allow
    plot customisation (e.g. Add/remove labels; Plot data  with  various
    combinations  of  lines, markers, and error bars; Change text fonts;
    Change X-axis  and/or  Y-axis;  Change  number  of  plotted  panels;
    Define and Fit models to data). Useful QDP Commands are:
    PLT> r x xlow xhigh             * Rescale X axis 
    PLT> r y ylow yhigh             * Rescale Y axis 
    PLT> r xlow xhigh ylow yhigh    * Rescale both
    PLT> log x                      * X axis is plot in logarithmic scale 
    PLT> log y                      * Y axis is plot in logarithmic scale
    PLT> log off                    * Turn off the logarithmic axes (both X and Y)
    PLT> dev /xxx                   * Change the current plot device 
    PLT> mo ?                       * List available model
    PLT> mo cons linr               * Define model= constant plus linear 
    plt> fit                        * Fit the defined model
    PLT> hardcopy filename          * Hardcopy of the current plot (postscript)
    PLT> exit                       * EXit: to exit from the PLT subroutine type:
    The  QDP/PLT  software  is  provided and maintained by Allyn Tennant
    (Marshall Space Flight Center). The PLT  software  uses  the  PGPLOT
    Graphics  Subroutine  Library  for plotting, written by T.J. Pearson
    (California Institute of Technology).
    
    
    
OUTPUT
    The analysis results are output in a FITS file. Two  different  FITS
    layouts  are available (see parameter outfiletype). The first stores
    one interval (or frame) of interval results per FITS table row,  and
    the  output file will have a single extension. The second stores one
    interval (or frame) per FITS extension, and  the  output  file  will
    have  as  many  extensions  as  the number of intervals (or frames).
    The output file contains, besides the array of results, a number  of
    statistical  variables  (and  errors if appropriate) associated with
    each interval (or frame)  for  each  time  series.   These  are:  1-
    average  count/s  in  frame  (in  a frame this is the average of the
    averages in  intervals);  2-  fractional  exposure  in  frame  (from
    average  of  fractional  exposures  in  intervals, the latter is the
    ratio  of  good  newbins   to   the   total   number   of   expected 
    newbins/interval);  3-variance  in  frame  (average  of variances in
    intervals); 4- expected variance in frame (average of  the  expected
    variances  in  intervals,  the  latter  is calculated from the error
    bars of the newbins);  5-  3rd  moment  in  frame  (average  of  3rd
    moments  in  intervals);  6-  minimum  count/s  in frame; 7- maximun
    count/s in frame; 8- excess variance in  frame  (average  of  excess
    variances    in    intervals,    the   latter   is   calculated   as  
    variance-expected variance); 9-  chi-square  in  frame  (average  of
    chi-squares  in  intervals);  10-rms  fractional  variation in frame
    (average of rms fractional variation in  intervals,  the  latter  is
    calculated  as the square root of the excess variance divided by the
    average.
    
    When "outfiletype"=2,  the  output  file  for  the  'crosscor'  task
    contains  in  each extension the following columns: time delay, half
    width of time delay bin, cross  correlation  and  error.   Not  many
    applications  can currently deal with the output files produced when
    "outfiletype"=1.  The format will be described in future releases.
    
    
PARAMETERS
    
    cfile1 (filename(s) first series+options) [string]
        Input filename(s) for the  first  time  series  +  options.  The
        valid  input  files  are  in  FITS  format  using  the  BINTABLE 
        extension.  Xronos  tasks  read  for  each  time   series   many 
        consecutive  input  files  (up to 50). Additional flexibility is
        provided by  Input  File  Options  which  are  used  to  perform
        algebraic  operations  on  individual input files (either on the
        'times' or on the 'count' or 'count/s' values). The  Input  file
        Options  are  also used to select columns and rows within a FITS
        file.  If the first character of the input string  is  '@',  the
        rest  of  the  string  is  taken to be a filename containing the
        list  of  input  files  (Filelist).  The  Filelist  can  contain 
        filenames   for   more  than  one  series.  See  description  of 
        "FILELIST and INPUT FILE OPTIONS".
    
    cfile2 (filename(s) second series) [string]
        As PARAMETER cfile1 (See description  of  "Filelist  format  and
        Input File Options").
    
    window (name of window file) [string]
        Filename  of the xronos window file. The window file is an ASCII
        file and by default a standard window file is used,  where  only
        exposure  windows  are  set.   To  modify  the  standard file or
        create a new file used the script XRONWIN.
    
    dtnb (integration time) [double]
        The duration in seconds of the NEWBIN  time.  For  binned  input
        files  the  NEWBIN  duration can not be shorter than the longest
        bin duration in the input file. In a number of XRONOS tasks  the
        NEWBIN  time  must  be an integer multiple of the minimum newbin
        time.   The  task  internally  calculates  (and  prints  on  the 
        screen)  a default value such that a single interval is produced
        with a fixed number of newbins (typically between 128  and  4096
        depending  on  the task and on the time interval length see also
        "nbdf" parameter).  Typing 'INDEF' forces the  task  to  use  as
        NEWBIN  time  the  value  calculated  by  the  program. NOTE: By
        pressing return the task will  use  as  NEWBIN  time  the  value
        found in the parameter file used in a previous run.
    
    nbint (number of points per interval) [integer]
        The  number  of  newbins  per interval used in the analysis. The
        "nbint" together with the NEWBIN duration determines the  length
        in  time  of  an  interval  and  therefore  the  total number of
        intervals  within  the  start  and  stop  time  over  which  the 
        analysis  will  be  carried out.  Typing 'INDEF' forces the task
        to use the default  value  (see  parameter  "nbdf").   NOTE:  By
        pressing  return  "nbint"  is  set  to  the  value  found in the
        parameter file used in a previous run.
    
    nintfm (number of intervals per frame) [integer]
        The results of the analysis from  individual  intervals  can  be
        averaged  to  produce  a frame.  The "nintfm" is used to specify
        the number of intervals averaged  in  a  frame.  Typing  'INDEF'
        forces  the task to use the default value (all intervals will be
        use in one frame).  NOTE: By pressing return "nintfm" is set  to
        the value found in the parameter file used in a previous run.
    
    itre (Flag for trend removal) [integer]
        A  polynomial  trend, up to 4th-order, can be removed from input
        time series.  Setting the parameter "itre" equal to 1 or 2 or  3
        or  4  remove  a  1st,  2nd,  3rd,  4th-order  polynomial trend,
        respectively.  The  trend  is  determined  separately  for  each 
        interval  of  each series by using a least-square technique. The
        value 0 does not cause the removal of any trend from  the  input
        series  and is the default value.  NOTE The trend removal is not
        available for the efold and efsearch tasks.
    
    itremo (Mode for trend removal) [integer]
        Specify how the trend removal is applied to the data  (available
        only  id  "itre" is higher than 0). The trend can be  subtracted
        from the time series (itremo =1) , or the  time  series  can  be
        divided  by  the  trend  (itremo = 2), or the time series can be
        replaced with the trend (itremo = 3). By default  the  trend  is
        subtracted (value set to 1).
    
    outfile (output filename) [string]
        Name  of the output file. If only the root is given, the program
        adds an extension of 3 characters, '.fXX', where  f  stands  for
        FITS  and  XX  is  a  suffix  which  identifies the program that
        creates the output. The XX values are  :  'ac'  (autocor),  'cc'
        (crosscor),  'ef  (efold),  'es' (efsearch), 'lc' (lcurve), 'ps'
        (powspec), 'ts' (timeskew). Typing '-'  forces  the  program  to
        generate   a   default   value  for  the  output  filename  (see 
        outfileroot  parameter).  By  typing  blank  characters  at  the 
        prompt no output file will be created.
    
    outfileroot (default value) [string]
        This  parameter  used  in conjunction with "outfile" generates a
        default output  filename.  If  the  value  of  "outfileroot"  is
        'default'  and  "outfile"  is '-', the output filename will have
        the same root name of the first input file of  the  fits  series
        with a '.fXX' extension (see outfile for XX values).
    
    outfiletype (Type of FITS layout) [integer]
        Define  the  FITS  structure  for the output file. Two types are
        available.  The first type (outfiletype=1)  has  1  interval  of
        results  per FITS table row.  The output file will have only one
        extension. Each row of the results column contains an  array  of
        values  with  a  size equal to the number of points per interval
        (or frame) and a number of rows equal to  the  valid  number  of
        intervals  analysed.   The  second  type  (outfiletype=2)  has 1
        interval of results per FITS extension.  The  output  file  will
        have  as  many  extension as the number of intervals (or frames)
        analysed.  The  column  containing  the  results  has  a  single 
        element  value  in  each  row and the number of rows is equal to
        the number of points in the  interval.   The  default  value  of
        "outfiletype" is 2 (one interval per FITS extension).
    
    plot (if plot) [boolean]
        Flag  specifying  whether or not the results of the analysis are
        plotted via PLT  (default  =  yes).  NOTE:  After  plotting  the
        results   the   XRONOS   task   is   left   in  the  interactive 
        plotting/fitting  mode  (PLT>  prompt)  use  command  `exit`  to 
        return  and  finish  the XRONOS task. If the "plot" parameter is
        set = no, the other queries regarding the plotting are  disabled
        ("plotdev", "plotfile", "plotdum").
    
    plotdev (device) [string]
        Change  the plot device. The most common plot devices are /xw (X
        window),  /tek  (tektronix),  /vt  (vt125),  /ps   (PostScript). 
        Setting  "plotdev" as '?', forces the program before plotting to
        list the available plot devices to the terminal  and  to  prompt
        for this parameter again.
    
    plotfile (.pco file) [string]
        Name of the Plt COmmands file.  For  each  task  an  appropriate
        default  Plt COmmand file is automatically loaded by the program
        setting the parameter "plotfile" as '-'.  The  user  can  insert
        additional commands using his  own  '.pco'  file at this level (
        or within the PLT> prompt).The user commands are appended to the
        default command file and therefore executed last. The    default
        '.pco' files are   stored   in   the   directory defined by  the
        parameter 'dpath'.
    
    tchat (terminal chattiness) [integer]
        Set  terminal  chattiness:  (0-4)  only  little  information  is 
        output in running XRONOS task ;  chattiness  5  is  the  default
        value;  (6-7)  more  details  on input files, windows, intervals
        statistics, etc.; (<8) mostly for debugging purposes.
    
    lchat (log file chattiness) [integer] 
        Set log file and chattiness in the log file: = 0  the  log  file
        is  not written; for all other values, information is written in
        the log file. The chattiness levels are  the  same  as  for  the
        terminal.
    
    logname (log filename) [string]
        Name for the log file. The default name is xronos.log.
    
    clobber  [boolean]
        Flag  specifying  whether  or  not  a pre-existing file with the
        same name as that requested for an output file  in  the  current
        task will be overwritten. Default value = yes.
    
    (dpath = XRDEFAULTS) [string]
        This  string  parameter  gives the path to the Xronos 'defaults'
        directory, which contains the  default  '.pco'  file  (used  for
        plotting)   and   the  defaults  window  file  'default_win.wi'. 
        Ordinarily, the user may leave this parameter set to the  string
        'XRDEFAULTS',   which  causes  Xronos  to  use  the  environment 
        variable XRDEFAULTS to locate these files. XRDEFAULTS is set  by
        the  mkftools  script  to point to the appropriate directory for
        the current distribution of Xronos  (for  FTOOLS  v3.6  this  is
        /ftools/xronos/defaults/).   If  the user wishes to modify these
        files, he or she may  make  and  edit  copies,  and  change  the
        XRDEFAULTS   variable   appropriately   using  setenv,  but  the 
        original files should not be changed.
    
    gapfill (running mean gap filling) [integer]
        Replace gaps in input series with  running  mean.   If  =0  (the
        default)  data  gaps  are not filled.  If =n newbin data gaps in
        input series are filled in with running mean  values  calculated
        over  n newbins. Note that a gap newbin is filled in only if the
        corresponding running mean is  calculated  over  n/4  points  at
        least  (this  means that in order to bridge a gap of m newbins n
        must be >1.35m).  This global  parameter  is  ignored  in  epoch
        folding applications (efold and efsearch).
    
    forcestart (flag for start time) [boolean]
        If  = yes the first interval will be forced to start at the time
        of the first time window  otherwise  (=no  default)  the  center
        time of the first qualified newbin is used as the start time.
    
    errorbars (Error bar Evaluation) [integer]
        This  parameter  defines  the way in which the error bars of the
        analysis results are calculated. If the number of the  intervals
        per   frame   ("nintfm")   is   higher  than  "errorbars"  value 
        (default=5), the error bars are evaluated by using the  standard
        deviation  of  the  average  (based  on  the  measured scatter).
        Otherwise the  error  bars  are  evaluated  by  propagating  the
        theoretical  error bars through an averaging process.  Note that
        for several XRONOS  applications  (e.g.  `autocor`,  `crosscor`)
        only  the former way of evaluating error bars is available.  For
        example, if "errorbars" is 5 in the application  `powspec`:  (a)
        if  a  frame  contains  the average of 5 or fewer power spectra,
        then the error bars  in  the  average  power  spectrum  will  be
        calculated  by  propagating  through the average the theoretical
        error  bars  associated  with  each  power  spectrum  (in   turn 
        obtained  from  the  relevant chi-square distribution); (b) if a
        frame contains the average of 6 or more power spectra, then  the
        error  bars  in the average power spectrum will be calculated by
        evaluating the standard deviation of the average power for  each
        frequency.    By  adjusting  the  value  of  "errorbars"  it  is 
        possible, e.g. to evaluate error bars as in  (a),  also  in  the
        case  in  which  a  large number of intervals per frame has been
        specified.  Values  <  5  are  not  recommended  (at  least  5-6 
        measures   are  necessary  to  reliably  evaluate  the  standard 
        deviation of the average from the scatter around it). NOTE:  not
        applicable for 'lcurve', 'lcstats' and 'efsearch'.
    
    exposure (flag for analysis of exposure profile) [boolean]
        If  =yes the exposure profile(s) (i.e. newbin values are set =1,
        gaps and rejected newbins are set =0) is/are  analysed  (instead
        of the input series). Default value is = no.
    
    normalization (type of normalization) [integer]
        Flag  to  specify  the  type  of  normalization  to apply to the
        results.  This parameter is  only  relevant  for  the  following
        tasks:   powspec,   autocor,  efold,  crosscor,  timeskew).  The 
        standard  normalization  corresponds  to  a  value  of  1   (the 
        default)  in  all XRONOS applications. Other normalization value
        flags are described for each  application  (See  normalization).
        NOTE: not applicable for 'lcurve' and 'efsearch'.
    
    simultaneous (flag for simultaneity) [boolean]
        If  =yes  a  strict  simultaneity  is  forced  between the input
        series in applications which use more then one series  (i.e.  if
        the  n-th  newbin  of a series is a gap or is rejected, then the
        n-th newbin of all other series will  be  also  rejected).  This
        flag  is  ignored  in the efold applications. Default value is =
        no.
    
    spwinbefore (special window start) [double]
        Special newbin window : number of seconds before. If a  value  >
        0  is used , e.g. 10.0, then all the newbins within 10.0 seconds
        before a newbin rejected by an intensity  window  will  also  be
        rejected.  The default (=0) is not to apply this type of special
        newbin window.
    
    spwinafter (special window stop) [double]
        Special newbin window : number of seconds after. If a  value  >0
        is  used  ,  e.g. 10.0, then all the newbins within 10.0 seconds
        after a newbin rejected by an  intensity  window  will  also  be
        rejected.  The default (=0) is not to apply this type of special
        newbin window.
    
    rescale (rescaling for results) [double]
        Rescaling factor applied to result  variables  and  errors.  The
        rescaling  is  applied just before writing the output file (this
        to avoid affecting the statistical  variables  for  the  frame).
        Default value for "rescale" is set to 1.
    
    offset (additive constant for results) [double]
        Additive  constant summed to result variables. Result error bars
        are left unchanged.  The additive constant is added just  before
        writing  the  output  file  (this  is  to  avoid  affecting  the 
        statistical variables for the frame). Note that if  a  rescaling
        factor  is  also  specified (different from 1), then the results
        are first multiplied by the rescaling factor. Default value  for
        "rescale" is set to 0.
    
    fast (Flag for fast algorithm) [boolean]
        This  parameter  sets the type of algorithm used for the Fourier
        transform.  IMPORTANT NOTE: This parameter can  be  set  by  the
        user  only  in the `powspec`, `autocor` and `crosscor` tasks (it
        is a query parameter in these tasks).  In all  the  other  tasks
        "fast"  is a non-query parameter, and should not be changed from
        the default setting.
    
    nser (Number of time series) [integer]
        Number  of   input   time   series   simultaneously   processed. 
        IMPORTANT  NOTE:  This  parameter,  the  values  of  which range
        between 1 and 4, can be set by the user  only  in  the  "lcurve"
        and  "efold" tasks (it is a query parameter in these two cases).
        In the other tasks "nser" is a non query parameter,  and  should
        not be changed from the default setting.
    
    ipow2 (Flag if power of 2) [integer]
        Internal  Flag used to decide if the current task must used with
        a power of 2 of number of points (ipow2=1) per interval  or  not
        (ipow2=0).  IMPORTANT NOTE: This parameter should not be changed
        by the user.
    
    iavgreb (Flag if average interval) [integer]
        Internal Flag used to decide if  the  current  task  allows  the
        averaging  of  intervals  in  frame  and/or the rebinning of the
        analysis results. If "iavgreb" is set to -1 the  results  in  an
        interval  can  not be either averaged or rebinned, if set to -2,
        the results in an interval can be  averaged  but  not  rebinned.
        IMPORTANT  NOTE:  This  parameter  should  not be changed by the
        user.
    
    nbdf (Default No. Bins) [integer]
        Set an internal default value for  the  number  of  newbins  per
        Interval.   This  value  is used to calculate the default newbin
        integration  time  to  have  one  interval  with  nbdf   points. 
        Different  "ndbf"  values  have  been  set  for different XRONOS
        task.  IMPORTANT  NOTE:  With  caution  this  parameter  can  be 
        changed by the user.
        
        
        
EXAMPLES
    
    1.  Given  2  time  series  with an original binning of 1 second and
    length 1.5 hours    compute the cross correlation  in  intervals  of
    1024  points and average all the results    per interval in a frame.
    Make a plot and output the results.
       > crosscor  cfile1="mydata1.lc" cfile2="myfile2.lc" window="-" dtnb=1 nbint=1024
         nintfm=INDEF plot=yes plotdev="/xw" outfile="-"
    
    2. As before but using as input file a list of filenames  (@all.lis)
       (see "Filelist and Input File Options").
       > crosscor cfile1="@all.lis"  window="-" dtnb=1 nbint=1024  nintfm=INDEF plot=yes
         plotdev="/xw" outfile="-"
    
    3.  Given  2  time  series  with an original binning of 1 second and
    length 1.5 hours    compute cross correlation using all the data  in
    one  interval  (nintfm=1).     The number of points in such interval
    length are 5400 and for the fast method this     requires  that  the
    number of points be a power of two. The closest value is 8192.
       > crosscor cfile1="@all.lis" window="-" dtnb=1 nbint=8192 nintfm=INDEF plot=yes
         plotdev="/xw" outfile="-"
    
    
    
SEE ALSO
    efold,   efsearch,  autocor,  powspec,  lcstats,  lcurve,  listdata, 
    timeskew xronwin, fits2qdp, ascii2lc.
    
    
BUGS
    Report     problems     to     angelini@lheavx.gsfc.nasa.gov     and    
    xanprob@athena.gsfc.nasa.gov.   Provide  a  detailed  description of
    the problem (with a log file if possible).

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Please send reports of errors to : xanprob@athena.gsfc.nasa.gov

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Last modified: Thursday, 06-May-2004 13:46:55 EDT