.help lcurve Jan96 xanadu.xronos
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NAME
lcurve  -- Produces binned lightcurves and plot up to 4 simultaneous 
energy time series. For multi-time series, ratio and sum are also calculated.
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USAGE
lcurve nser file(s)+options window dtnb nbint outfile plot plotdev 
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DESCRIPTION
This task produces lightcurves, plots and outputs the results (in a FITS file). 
The input file format is FITS using the BINTABLE extension. Both binned data format 
and event format are input. Up to 4 simultaneous time series can be input (See FILELIST 
and INPUT FILE OPTIONS) and ratios and sums are calculated (for more that 2 input series).
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 standard plot output is counts/sec versus time, but for multiple time series the 
hardness and colour-colour diagrams are available where appropriate. The plotting is 
performed through PLT, and further plot manipulation or data fitting can be done from the
PLT prompt (See also PLOT). The analysis results are written, if specified, into a 
FITS file (See OUTPUT file). The guidelines of the FITS input file are described in 
in Legacy journal volume 3. 
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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. 

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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 :
.nf
 * 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 
.fi
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.
 
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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. 
.nf
 file1_ser1
 file2_ser1
 ///
 file1_ser2
 file2_ser2
 ///
 file1_ser3
 file2_ser3
.fi
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 :
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 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.
.fi

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:

.nf
 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 
.fi 
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.

.nf
 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    "    "    "         "    "    "     "  "   "          " 
.fi

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PLOT
The array of results from each XRONOS task can be plotted. The PLT routine (See also 
the 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. For programs that handle simultaneously more than one time series, 
e.g. lcurve and efold, different types of analysis results can be plotted depending on the 
number of input time series. For two input time series three different plots are provided 
(1) the sum of the intensities of the two input series on the X-axis and on the Y-axis 
the count ratio (ser2/ser1) of the two input series (Hardness-plot); (2) Time (or Phase) on the 
X-axis and the intensity on the Y-axis for the two input time series; (3) As (2) but also 
the ratio is plotted. For three or four input time series two different plots are available:
(1) Colour-Colour diagram that shows the ratio of ser3/ser2 or ser4/ser3 on the Y-axis 
(for 3 or 4 input series respectively) and ser2/ser1 (always) on the X-axis; (2) Time (or Phase)
on the X-axis and the intensity on the Y-axis for the 3 (or 4) input time series.
The choice of the plot type is done by setting the parameter "plotnum". 
Note that for the multicolor tasks all the arrays calculated by lcurve or efold are 
available in 'PLT>'. When 3 or 4 series are input, a color ratio plot versus time (or phase),
not available in the standard options, can be obtained as follows.
At the prompt 
.nf
 Two plotting styles available:
 Colour-Colour [1] ; Intensity vs Time (or Phase)[ # of series (3 or 4)];
Enter PLOT style number (default=1)[]
.fi
enter the number of time series. On the screen the plot has as many panels
as many input series, showing the counts for each series on the Y-axis and time or 
phase on the X-axis. At the 'PLT>' prompt type 'info' which gives the list of arrays
available. For example for 3 input series the info command gives 
.nf
PLT> info

 Scales:
 Grp  Wind    Label     XData Min    XData Max    YData Min    YData Max
  1    -1  Time (s)   :  3496.    ,   8646.     :  3496.    ,   8646.
  2     2  Ser 1      :  3496.    ,   8646.     :  331.8    ,   466.4
  3     3  Ser 2      :  3496.    ,   8646.     :  415.9    ,   613.8
  4     4  Ser 3      :  3496.    ,   8646.     :  747.7    ,   1080.
  5    -1  Ser 2/Ser  :  3496.    ,   8646.     :  1.222    ,   1.325
  6    -1  Ser 3/Ser  :  3496.    ,   8646.     :  1.755    ,   1.819
  7    -1  Ser 1+2+3  :  3496.    ,   8646.     :  1495.    ,   2160.
  8    -1             :  3496.    ,   8646.     :  1.000    ,   1.000
PLT>
.fi     
To plot the ratios (array number 5 and 6) versus time together with the 
three input lightcurves use the following commands: 
.nf
PLT> color 1 on 5 6 
PLT> plot ver
PLT> plot
.fi
The final plot will contain 5 panels. The first three are the input series 
the last two the ratios. 

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:
.nf
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:
.fi
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).

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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.

The output for the 'lcurve' task consists of time and counts/s vectors (with associated error 
columns). There are as many count/s vectors as there are time series analysed (therefore up to 4). 
The time column always contains number of seconds from the keyword TIMEZERO (or TIMEZERI and 
TIMEZERF). The time in the output (TIME(n)+TIMEZERO) is in TJD (TJD=  JD-2440000.5) if the input light
curves have the MJDREF keyword present in the header, otherwise the original times are maintained.
Note that the TIMESYS keyword in either cases is not currently set.
For 2 input series the additional columns contain the ratio (ser2/ser1) and the sum 
(ser1+ser2) of the input series and their errors. For 3 input series the additional columns contain 
two ratios (ser2/ser1 and ser3/ser2) and the sum (ser1+ser2+ser3) and their errors. 
For 4 input series the additional columns contain two ratios (ser2/ser1 and ser4/ser3) and 
the sum (ser1+ser2+ser3+ser4) and their errors. The output also contains a fractional exposure 
column (currently is filled with values different from 1 for only 1 input series)
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PARAMETERS
.ls 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.
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.ls 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".
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.ls cfile2 (filename(s) second series) [string]
As PARAMETER file1 (See description of "Filelist format and Input File Options").
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.ls cfile3 (filename(s) third series) [string]
As PARAMETER file1 (See description of "Filelist format and Input File Options").
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.ls cfile4 (filename(s) fourth series) [string]
SEE PARAMETER file1 (See description of "Filelist format and Input File Options").
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.ls 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.
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.ls 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.
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.ls 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.
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.ls 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.
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.ls 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).
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.ls tunits (Time units for plot) [integer]
Five different time axis units can be specified: (0) seconds from the start
time of the current interval (which might be different from the time of the first
accepted newbin) (1) seconds from the start of the hour, (2) hours from the
start of the day, (3) days, (4) seconds from the start time of the first
interval. Option 4 is useful when the lightcurve is broken into several intervals
and it is desirable to maintain for each plotted interval the same counter (from the 
start time of the first interval) for the time axis.
The default depends on the duration of the input series and is printed on the screen. 
Typing 'INDEF' forces the task to use the calculated value.
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.ls 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.
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.ls 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).
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.ls 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).
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.ls 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").
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.ls 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.
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.ls 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'.
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.ls plotdnum (Style of plots) [integer] 
The parameter sets the plot style which appear on the plotting device.
For 2 input series, three different plots are available: 1) Total intensity
on X-axis and Ratio on Y-axis (Hardness), 2) Time (or Phase) on the X-axis 
and intensity of the 2 input series on the Y-axis, and 3) as 2 but also the 
ratio is plotted. The parameter "plotdnum" should be set equal to 1 or 2 or 3 
respectively to get one of the three style plots. For 3 or 4 input series only two 
style of plots are available : 1) Colour-Colour diagram (ratio 1 vs ratio 2)
and 2) Time (or phase) on the X-axis and intensity of the 3 (or 4) input series
on the Y-axis. The parameter "plotdnum" should be set equal to 1 or to the total 
number of input timeseries (e.g. 3 or 4) respectively to get one of the two 
style plots. 
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.ls 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.
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.ls 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.
.le
.ls logname (log filename) [string]
Name for the log file. The default name is xronos.log.
.le 
.ls 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.
.le
.ls (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.
.ls 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).
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.ls 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.
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.ls 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'. 
.le
.ls 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.
.le
.ls 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'.
.le
.ls 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.
.le
.ls 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.
.le
.ls 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.
.le
.ls 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.
.le
.ls 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.
.le
.ls 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.
.le
.ls 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.
.le
.ls 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.
.le
.ls 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.

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EXAMPLES
1. From a single file data (1 time series) with a binning of 20 seconds and a start-stop=5000
   seconds, create a one interval lightcurve with a binning of 100 seconds. 
   Make a plot and output the results.

   > lcurve nser=1 cfile1="mydata.lc" window="-" dtnb=100 nbint=50 outfile="-"
     plot=yes plotdev="/xw" 

2. From 3 input series with a binning of 20 seconds and a length of 5 hours, create a 
   one-interval lightcurve with a binning of 400 seconds. Plot the Colour-Colour diagram 
   and not create an output. 

   > lcurve nser=3 cfile1="@all.lis" window="-" dtnb=400 nbint=45 outfile=" "
     plot=yes plotdev="/xw"  plotdnum=1

   The parameter cfile1 is a file containing the list of filenames of each series 
   (see "Filelist and Input File Options").
    
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SEE ALSO
efold, efsearch, crosscor, autocor, powspec, lcstats, listdata, timeskew
xronwin, fits2qdp, ascii2lc.
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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).
