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SUBROUTINE DDET3

PURPOSE
   TO COMPUTE A VECTOR OF DERIVATIVE VALUES GIVEN A VECTOR OF
   FUNCTION VALUES WHOSE ENTRIES CORRESPOND TO EQUIDISTANTLY
   SPACED ARGUMENT VALUES.

USAGE
   CALL DDET3(H,Y,Z,NDIM,IER)

DESCRIPTION OF PARAMETERS
   H	 -  DOUBLE PRECISION CONSTANT DIFFERENCE BETWEEN
	    SUCCESSIVE ARGUMENT VALUES (H IS POSITIVE IF THE
	    ARGUMENT VALUES INCREASE AND NEGATIVE OTHERWISE)
   Y	 -  GIVEN VECTOR OF DOUBLE PRECISION FUNCTION VALUES
	    (DIMENSION NDIM)
   Z	 -  RESULTING VECTOR OF DOUBLE PRECISION DERIVATIVE
	    VALUES (DIMENSION NDIM)
   NDIM  -  DIMENSION OF VECTORS Y AND Z
   IER	 -  RESULTING ERROR PARAMETER
	    IER = -1  - NDIM IS LESS THAN 3
	    IER =  0  - NO ERROR
	    IER =  1  - H = 0

REMARKS
   (1)	 IF IER = -1,1, THEN THERE IS NO COMPUTATION.
   (2)	 Z CAN HAVE THE SAME STORAGE ALLOCATION AS Y. IF Y IS
	 DISTINCT FROM Z, THEN IT IS NOT DESTROYED.

SUBROUTINES AND FUNCTION SUBPROGRAMS REQUIRED
   NONE

METHOD
   IF X IS THE (SUPPRESSED) VECTOR OF ARGUMENT VALUES, THEN
   EXCEPT AT THE ENDPOINTS X(1) AND X(NDIM), Z(I) IS THE
   DERIVATIVE AT X(I) OF THE LAGRANGIAN INTERPOLATION
   POLYNOMIAL OF DEGREE 2 RELEVANT TO THE 3 SUCCESSIVE POINTS
   (X(I+K),Y(I+K)) K = -1,0,1.	(SEE HILDEBRAND, F.B.,
   INTRODUCTION TO NUMERICAL ANALYSIS, MC-GRAW-HILL, NEW YORK/
   TORONTO/LONDON, 1956, PP.82-84.)