SUBROUTINE SPLINT(XA,YA,Y2A,N,X,Y,YPRIM)
      INTEGER N
      REAL*8 XA(N),YA(N),Y2A(N), X,Y,YPRIM

* Calculate Y(X) from spline XA,YA,Y2A
*
* XA(N),YA(N) = pivoting points,
* Y2A(N) = 2nd deriviatives in points.

      INTEGER K,KLO,KHI
      REAL*8 A,B,H

      KLO=1
      KHI=N

1     IF (KHI-KLO.GT.1) THEN
        K=(KHI+KLO)/2
        IF(XA(K).GT.X)THEN
          KHI=K
        ELSE
          KLO=K
        ENDIF
        GOTO 1
      ENDIF

      H=XA(KHI)-XA(KLO)
      IF (H.LE.0.) THEN
         call nmf_error ('Inputs to SPLINT not prperly sorted')
      ENDIF

      A=(XA(KHI)-X)/H
      B=(X-XA(KLO))/H
      Y=A*YA(KLO)+B*YA(KHI)+
     *      ((A**3-A)*Y2A(KLO)+(B**3-B)*Y2A(KHI))*(H**2)/6.
      YPRIM= (YA(KHI)-YA(KLO) +
     &         (Y2A(KHI)*(3*B**2-1.) - Y2A(KLO)*(3*A**2-1.))/6.
     &       ) / H
      RETURN
      END