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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. Zones 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 2020-04-08