      SUBROUTINE MAX(X,N,IWRITE,XMAX)
C
C     PURPOSE--THIS SUBROUTINE COMPUTES THE
C              SAMPLE MAXIMUM 
C              OF THE DATA IN THE INPUT VECTOR X. 
C     INPUT  ARGUMENTS--X      = THE SINGLE PRECISION VECTOR OF
C                                (UNSORTED OR SORTED) OBSERVATIONS.
C                     --N      = THE INTEGER NUMBER OF OBSERVATIONS
C                                IN THE VECTOR X. 
C                     --IWRITE = AN INTEGER FLAG CODE WHICH 
C                                (IF SET TO 0) WILL SUPPRESS
C                                THE PRINTING OF THE
C                                SAMPLE MAXIMUM
C                                AS IT IS COMPUTED;
C                                OR (IF SET TO SOME INTEGER 
C                                VALUE NOT EQUAL TO 0),
C                                LIKE, SAY, 1) WILL CAUSE
C                                THE PRINTING OF THE
C                                SAMPLE MAXIMUM
C                                AT THE TIME IT IS COMPUTED.
C     OUTPUT ARGUMENTS--XMAX   = THE SINGLE PRECISION VALUE OF THE
C                                COMPUTED SAMPLE MAXIMUM.
C     OUTPUT--THE COMPUTED SINGLE PRECISION VALUE OF THE
C             SAMPLE MAXIMUM. 
C     PRINTING--NONE, UNLESS IWRITE HAS BEEN SET TO A NON-ZERO
C               INTEGER, OR UNLESS AN INPUT ARGUMENT ERROR
C               CONDITION EXISTS.
C     RESTRICTIONS--THERE IS NO RESTRICTION ON THE MAXIMUM VALUE
C                   OF N FOR THIS SUBROUTINE.
C     OTHER DATAPAC   SUBROUTINES NEEDED--NONE.
C     FORTRAN LIBRARY SUBROUTINES NEEDED--NONE.
C     MODE OF INTERNAL OPERATIONS--SINGLE PRECISION.
C     LANGUAGE--ANSI FORTRAN. 
C     REFERENCES--DAVID, ORDER STATISTICS, 1970, PAGE 7.
C     WRITTEN BY--JAMES J. FILLIBEN
C                 STATISTICAL ENGINEERING LABORATORY (205.03)
C                 NATIONAL BUREAU OF STANDARDS
C                 WASHINGTON, D. C. 20234
C                 PHONE:  301-921-2315
C     ORIGINAL VERSION--JUNE      1972. 
C     UPDATED         --SEPTEMBER 1975. 
C     UPDATED         --NOVEMBER  1975. 
C
C---------------------------------------------------------------------
C
      DIMENSION X(1)
C
      IPR=6
C
C     CHECK THE INPUT ARGUMENTS FOR ERRORS
C
      IF(N.LT.1)GOTO50
      IF(N.EQ.1)GOTO55
      HOLD=X(1)
      DO60I=2,N
      IF(X(I).NE.HOLD)GOTO90
   60 CONTINUE
      WRITE(IPR, 9)HOLD
      XMAX=X(1)
      GOTO101
   50 WRITE(IPR,15) 
      WRITE(IPR,47)N
      RETURN
   55 WRITE(IPR,18) 
      XMAX=X(1)
      GOTO101
   90 CONTINUE
    9 FORMAT(1H ,109H***** NON-FATAL DIAGNOSTIC--THE FIRST  INPUT ARGUME
     1NT (A VECTOR) TO THE MAX    SUBROUTINE HAS ALL ELEMENTS = ,E15.8,6
     1H *****)
   15 FORMAT(1H , 91H***** FATAL ERROR--THE SECOND INPUT ARGUMENT TO THE
     1 MAX    SUBROUTINE IS NON-POSITIVE *****)
   18 FORMAT(1H ,100H***** NON-FATAL DIAGNOSTIC--THE SECOND INPUT ARGUME
     1NT TO THE MAX    SUBROUTINE HAS THE VALUE 1 *****)
   47 FORMAT(1H , 35H***** THE VALUE OF THE ARGUMENT IS ,I8   ,6H *****)
C
C-----START POINT-----------------------------------------------------
C
      XMAX=X(1)
      DO100I=2,N
      IF(X(I).GT.XMAX)XMAX=X(I)
  100 CONTINUE
C
  101 IF(IWRITE.EQ.0)RETURN
      WRITE(IPR,999)
      WRITE(IPR,105)N,XMAX
  105 FORMAT(1H ,26HTHE MAXIMUM OF THE SET OF ,I6,17H OBSERVATIONS IS ,E
     115.8)
  999 FORMAT(1H )
      RETURN
      END 
