REAL FUNCTION CV(XVAL,NDATA,NCONST,NORD,NBKPT,BKPT,W)
C***BEGIN PROLOGUE  CV
C***REFER TO  FC
C
C     This is a companion function subprogram for FC( ).
C     The documentation for FC( ) has more complete
C     usage instructions.
C
C      Evaluate the variance function of the curve obtained
C      by the constrained B-spline fitting subprogram, FC( ).
C
C     Revised Feb. 14, 1979.
C***ROUTINES CALLED  BSPLVN,SDOT
C***END PROLOGUE  CV