Identifier   sm_airy

 Purpose      Smooth SPD or AAR using a lorentzian filter

 Synopsis     out = sm_airy(in, width [,band] [,det] [,/sample] [,/velo] 
                            [,/sep][,stat=stat])

 Arguments    Name   I/O Type:       Description:
              ---------------------------------------------------------------------
              in      I  AAR/SPD      spectrum to be smoothed
              width   I  float        FWHM of lorentzian used for smoothing,
                                      In wavelength [um] by default.
              band    I  int scalar/  Option to select one band (scalar) or several 
                         array        (array). Example: band=2, band=[1,4].
                                      If absent all bands are selected (default).
                                      Illegal option for LAAR.
              det     I  int scalar/  Option to select one detector (scalar) or 
                         array        several (array). Example: det=6, det=[3,21,30].
                                      If absent all detectors are selected (default).
              /sample I  switch       if set, the width is interpreted in terms
                                      of samples
              /velo   I  switch       if set, the width is interpreted in terms
                                      of velocity [km/s]
              /sep    I  switch       if set smoothing is done separately
                                      for each detector
              stat   I/O int          error status, 0 if ok, 1 if fatal

 Returns      Smoothed AAR/SPD

 Description  Smooth fluxes in a SPD or AAR by convolution with a Lorentz 
              profile cut off at 3*FWHM (on either side, 3% of peak value). At edges, 
              signal and error are set to zero (within 3*FWHM of edges). When 
              (2*3*FWHM + 1) is longer than the signal, this latter and the error are 
              set to 0. The FWHM of the lorentzian can be specified in wavelength 
              (default), velocity units or sample domain. In the first 2 cases data is 
              unequally sampled. For AAR, smooth over all detectors combined together 
              (default) or separately on each detector when keyword /sep is set.
              The errors are propagated from the original data.

 Comment      Does not treat sdir nor scnt. Does not handle SPDs.
              It is too difficult to have this deal with SWS SPD offsets?
              How to apply to SPDs???? even after RESUM???
              The program would have to know which SPD fluxes are the good 
              ones (i.e. those with reset).

 Example      --

 Dependencies   CALLS: chk_tag, is_struct, sap_error, sap_keyword_set,
                       update_history
                CALLED FROM: IA, GUI

 Category     ISAP

 Filename     sm_airy.pro

 Author       Laurent Verstraete (IAS) (-->LV)

 Version      1.3 

 History      Draft reqs                    DL/ES/CW  27.7.95
              revision of requirements      E. Sturm   8.8.95 
              1.0 - 04.03.96  LV  creation
              1.2 - 19.03.96  LV  modified to handle combined or separate sets 
                                  of band/det. Treat all AARs. Make wavelengths 
                                  ascendent.
              1.3 - 12.3.96   ES  stat added
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