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        LAS\BASE [Deg] [/PLOT [Ipen]] [/INDEX] [/OBS] [/CONTINUUM [Flux]]
        LAS\BASE SINUS Amplitude Period Phase [/PLOT [Ipen]]
        LAS\BASE LAST [/PLOT [Ipen]]

    When  working  on  single  spectra, BASE copies R into T, then subtracts
    from R a polynomial baseline of degree Deg, or a sinusoidal baseline  if
    the first argument is SINUS. Polynomial baseline degree must be in range
    0-100. Areas defined by the SET WINDOW command are not used to  fit  the
    baseline. The T content may be recovered with SWAP.

    BASE SINUS Amplitude Period Phase
    (Phase  is in the same unit as the period, usually km/s or MHz) Subtract
    a sinusoid. Minimization will be done including also a  linear  baseline
    in addition to the sinusoid.

    Use  the last determined baseline instead of computing a new one. It can
    be useful to find a baseline from one backend and apply it  to  another.
    This  also applies for sinusoidal baselines. 0th and 1st order polynomi-
    als, and sinus fit are extrapolated if the R spectrum extends beyond the
    LAST spectrum limits. 2nd order (and higher) polynomials are not extrap-
    olated and the edge values are used beyond the LAST spectrum limits.

    Plot this baseline after the minimization, using the Ipen-th pen proper-
    ties. The pencil 2 (red at startup) is used by default.

    Subtracts  a  baseline to all records that have been loaded. This option
    is not needed if SET ACTION INDEX. /PLOT and /INDEX options  are  incom-

    indicate  that  the baseline is to be fitted to the current R buffer ob-
    servations. This option is not needed if the action level  is  OBS  (de-
    fault). /OBS and /INDEX are incompatible.


    1) Divide the spectrum by the baseline (rather than subtracting it), and
    then 2) multiply by the average flux. This is useful to keep the contin-
    uum level, when continuum is present and variations of atmospheric emis-
    sion are properly subtracted out by fast enough switching.  This  is  of
    course the case for correlation spectra (e.g. coming from an interferom-
    eter). The continuum level will be adjusted to the value of the argument
    `Flux', if present; e.g. /CONTINUUM 1.0 will produce a spectrum of line-
    to-continuum ratio. BASE /CONTINUUM does not work with BASE LAST or BASE

Gildas manager 2020-10-13