CALL SEQUENCE...
      spdlon  SPFILE LONDER OUTPUT
 
 
      DESCRIPTION...
      spdlon  - SPECTRAL LONGITUDE DERIVATIVE OF A SPECTRAL ARRAY
 
 
      AUTHOR  - B.Dugas, RPN, FEB 08/94.
      LAST REVISION: $Header: /home/cvs/RMNLIB/utils/rdiag/lspgm/spdlon.ptn,v 4.7 2014/09/25 20:20:53 dugas Exp $
 
 
      PURPOSE - READS A FILE OF SPECTRAL COEFFICIENTS (SPFILE), CONVERTS
                THEM TO THE LONGITUDE DERIVATIVE BY MULTIPLYING BY IM.
 
 
      INPUT FILE...
       SPFILE = INPUT FILE OF SPECTRAL COEFFICIENTS
 
      OUTPUT FILE...
       LONDER = OUTPUT FILE OF SPECTRAL LONGITUDINALLY DERIVED ARRAYS
 
 
 
 
      EXIT CONDITIONS...
        0 NO PROBLEMS
        1 PREMATURE EOF ON SPFILE
        2 INTERNAL SPECTRAL REPRESENTATION ERROR
        3 LM GREATER THAN MAXM (999)
        4 ERROR READING SPFILE. CHANGING SIZE