Identifier   dered_getext

 Purpose      Function to interpolate extinction or tau for a certain lambda

 Synopsis     out = dered_getext(lawlam,lawext,lambda,iguess,stat)

 Arguments    Name   I/O Type:     Description:
              ----------------------------------------------------------
              lawlam  I  fltarr    array with wavelengths
              lawext  I  fltarr    array with values for these wavelengths
              lambda  I  float     wavelength for which to get interpolated
                                   value
              iguess I/O int       index of last hit. speeds up search
                                   if wavelengths are monotonically increasing.
                                   is updated during execution
              stat    O  int       error status, 0 if ok, 1 if fatal error

 Returns      interpolated value
              0 if fatal error occured

 Description  

 Comment

 Example      exv = dered_getext(lawlam,lawext,0.55,iguess,stat)

 Dependencies  CALLS: sap_error
               CALLED FROM: dered, dered_corr

 Category     ISAP

 Filename     dered_getext.pro

 Author       D.Lutz

 Version      1.0

 History      0.1 12-10-95 DL
              0.2 18-10-95 DL use sap_error instead of error
              1.0 30-11-95 ES V1 delivery
              1.1 29-02-96 ES stat added
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Copyright (C) 1995, Max-Planck-Institut fuer extraterrestrische Physik (MPE);
                    Garching, Germany                                       ;
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