SUBROUTINE CDPLFN (
*
*  inputs
*
     :                  VAR, COEFF,
*
*  outputs
*
     :                  F0, FVAR, FCOEFF)
*
*  Module number:
*
*  Module name:
*
*  Keyphrase:
*  ----------
*  Calculate functional values and derivatives of a plane in 3-D
*
*  Description:
*  ------------
*  For the function:
*
*       F = A * X + B * Y + C - Z
*
*  calculate the functional value F0, for given A, B, C, X, Y, and Z.  Also
*  calculate the partial derivatives of F relative to A, B, C
*  (coefficents) and X, Y, and Z (variables).
*
*  COEFF(1) = A, COEFF(2) = B, COEFF(3) = C, VAR(1) = X, VAR(2) = Y, VAR(3) = Z
*
*  FORTRAN name: CDPLFN.FOR
*
*  Keywords of accessed files and tables:
*  --------------------------------------
*  Name                         I/O     Description / Comments
*       None
*
*  Subroutines Called:
*  -------------------
*  CDBS:
*       None
*  SDAS:
*       None
*  Others:
*       None
*
*  History:
*  --------
*  Version      Date        Author          Description
*     1       02-16-87     J.-C. HSU        design and coding
*
*-------------------------------------------------------------------------------
*
*== input:
*                                       --observed variables at a given point
*                                       --(e. g. X and Y coordinates)
        DOUBLE PRECISION        VAR(*),
*                                       --coefficients in the given function
     :                          COEFF(*)
*
*== output:
*                                       --functional value
        DOUBLE PRECISION        F0,
*                                       --partial derivativeS relative to the
*                                       --variables and coefficients
     :                          FVAR(*), FCOEFF(*)
*
*------------------------------------------------------------------------------
*
*  functional value
*
        F0 = COEFF(1) * VAR(1) + COEFF(2) * VAR(2) + COEFF(3) - VAR(3)
*
*  partial derivatives relative to the variables
*
        FVAR(1) = COEFF(1)
*
        FVAR(2) = COEFF(2)
*
        FVAR(3) = -1.D0
*
*  partial derivatives relative to the coefficients
*
        FCOEFF(1) = VAR(1)
*
        FCOEFF(2) = VAR(2)
*
        FCOEFF(3) = 1.D0
*
        RETURN
        END