;-------------------------------------------------------------
;+
; NAME:
;      F_CBC
; PURPOSE:
;      This function, calculates the weighting coefficients 
;      for the cubic convolution interpolation.
; CATEGORY:
;      MATHEMATICAL
; CALLING SEQUENCE:
;      aj = f_cbc(ox,oxj,oh)
; INPUTS:
;      ox = The x-value at which you are interpolating using
;        cubic convolution.
;        type: scalar,integer or floating point
;      oxj = A vector containing the given x values.
;        type: scalar,integer or floating point
;      oh = The value of one unit length interval.
;        type: scalar,integer or floating point
; KEYWORD PARAMETERS:
; OUTPUTS:
;      aj = A vector containing the weighting coefficients
;        for the cubic convolution interpolation.
;        type: scalar,integer or floating point
; COMMON BLOCKS:
; NOTES:
; MODIFICATION HISTORY:
;      H. Cohl,   5 Feb, 1991 --- Initial implementation.
;-
;-------------------------------------------------------------

function f_cbc,ox,oxj,oh,help=help

  ;Display idl header if help is required.
  if keyword_set(help) or n_params() lt 3 then begin
    get_idlhdr,'f_cbc.pro'
    aj=-1
    goto,finishup
  endif

  ;Convert values to floating point.
  x=ox*1.
  xj=oxj*1.
  h=oh*1.
  aj=oxj

  ;Calculate distances of xj to x.
  z=abs((x-xj)/h)

  for i=0,4 do begin
    if (z(i) le 1.) then aj(i)=1.-(2.5*z(i)^2)+(1.5*z(i)^3) else $
    if (z(i) le 2.) then aj(i)=2.-(4.*z(i))+(2.5*(z(i)^2))-(0.5*(z(i)^3)) else $ 
    aj(i)=0.
  endfor 

  finishup:

return,aj 

end