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        LAS\EXTRACT [X1 X2 [Unit]] [/INDEX]

    In its default mode, EXTRACT copies R into T, extracts a  subsection  of
    R,  and save the result in R. If the option /INDEX is present, or if SET
    ACTION is INDEX, a subsection of each observation in the  index  is  ex-
    tracted and saved in the output file.

    Without  arguments,  the  cursor is invoked (if available) to define the
    subsection range. If the arguments X1 and X2 are present, the subsection
    is  defined  by  this range, in the given Unit (if any) or by default in
    the current X axis unit (SET UNIT). X2 can be indifferently  greater  or
    lower  than  X1,  and  Unit  is a single character in the four C)hannel,
    V)elocity, F)requency or I)mage. Note that if Unit is F or I, the number
    of extracted channels can vary for two similar observations (same setup)
    because of different Doppler factors.

    If the range overlaps the input spectrum limits, a warning is raised and
    the  missing  data is filled with the blanking value. Requesting a range
    off the input spectrum is an error. The command FIND /FREQUENCY can help
    you  to  build  an  index  with spectra overlapping one frequency or one
    range of frequencies.

    On return, the observation header is consistently updated: the reference
    channel  is  shifted  and  number  of channels updated. The PLOT section
    (which remembers the previous plotting limits) is  disabled  because  it
    probably does not makes sense for the extracted data array.

    Only regularly sampled X axes are supported.

Gildas manager 2020-10-13