C	M.R. BROWN
C	SHELL SORT ROUTINE
C	TAKEN FROM THE ELEMENTS OF PROGRAMMING STYLE
C		BY KERNIGHAN AND PLAUGER
C		PP 109
C
	SUBROUTINE SHELL(X,N)
	DIMENSION X(N)
C  SORTS UP. IF THERE ARE NO EXCHANGES (IEX=0) ON A SWEEP
C  THE COMPARISON GAP (IGAP) IS HALVED FOR THE NEXT SWEEP
	IGAP=N
5	IF(IGAP.LE.1)RETURN
	IGAP=IGAP/2
	IMAX=N-IGAP
10		IEX=0
		DO 20 I=1,IMAX
			IPLUSG=I+IGAP
			IF(X(I).LE.X(IPLUSG))GO TO 20
			  SAVE=X(I)
			  X(I)=X(IPLUSG)
			  X(IPLUSG)=SAVE
			  IEX=IEX+1
20		CONTINUE
		IF(IEX.GT.0)GO TO 10
	GO TO 5
	END