function coeffderiv, coeff

; NAME:
;     COEFFDERIV
;
; PURPOSE:
;     To calculate the coefficients of the derivative of a polynomial given 
;     its coefficients.
;
; CATEGORY:
;     Data Reduction
;
; CALLING SEQUENCE:
;     derivative coefficients = coeffderiv(coeff)
;
; INPUTS:
;     coeff - A floating point vector containing coefficients of a polynomial, 
;	      which the user wishes to differentiate.
;
; OUTPUTS:
;     Returns a floating point vector containing the coefficients of the 
;     derivative of the polynomial specified by the input coefficients.
;
; KEYWORD PARAMETERS:
;     None.
;
; PROCEDURES CALLED:
;     None.
;
; PROCEDURE:
;     The coefficients of the derivative are calculated using the rule 
;     d(C*x^n)/dx = n*C*x^(n-1).
;
; COMMON BLOCKS:
;     None.
;
; SIDE EFFECTS:
;     None.
;
; RESTRICTIONS:
;     None.
;
; MODIFICATION HISTORY:
;     2002-04-08 - Written by J. R. Leong, Institute for Astronomy, UH at 
;		   Manoa.

; Check the calling statement.

if n_params() lt 1 then begin

    print, 'function - derivative coefficients = coeffderiv(coeff)'
    return, -1

endif

; Calculate the derivative coefficients.

size = size(coeff)
powers = indgen(size[1])

derivcoeff = powers*coeff
derivcoeff = derivcoeff[1:*]

return, derivcoeff

end