NAME:
    sinterp4
 PURPOSE: (one line)
    Four-fold sinc interpolation of a vector of data.
 DESCRIPTION:
    This function will do a 4-fold sinc interpolation of the data
    array that is passed.
 CATEGORY:
    Numerical
 CALLING SEQUENCE:
    result = sinterp4( x )
 INPUTS:
    x     : Input data array.
 OPTIONAL INPUT PARAMETERS:

 KEYWORD PARAMETERS:

 OUTPUTS:
    The interpolated array is returned as the function value.
 COMMON BLOCKS:

 SIDE EFFECTS:

 RESTRICTIONS:

 PROCEDURE:

 MODIFICATION HISTORY:
    Original C-Language version written by: Marc W. Buie, Institute for
 Astronomy, University of Hawaii.  Date: 9 December 1987.
    Adapted for IDL by Doug Loucks, Lowell Observatory, September 2, 1993.