**==sum.f  
C++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
C
C*************************
C**       SUM           **
C*************************
C
C
      REAL  FUNCTION  SUM (X,SKIP,N)
C
C Purpose: To add up n elements of the vector x, skipping 'skip' elements
C          between each addition
C
      INTEGER  SKIP, N
      REAL     X(SKIP,N)
C
C====== LOCALS:
C
      INTEGER  I
C
C------------------------------------------------------------------------------
C
      SUM = 0.0
      DO 20 I = 1 , N
         SUM = SUM + X(1,I)
 20   CONTINUE
      RETURN
      END
