SUBROUTINE PLOT(NPLOTS, NPTS, PTS, LABELS, XCHARS, OUNIT)
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C   PURPOSE
C   -------
C
C      PRODUCES A SCATTER PLOT OF SEVERAL Y VARIABLES VS. ONE X VARIABLE
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C   DESCRIPTION
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C   1.  THE X-VALUES ARE STORED IN THE FIRST COLUMN OF THE ARRAY PTS,
C       AND THE Y-VALUES ARE STORED IN THE SECOND COLUMN OF THE ARRAY
C       PTS.  THE LABELS FOR THE X-AXIS ARE STORED IN THE FIRST COLUMN
C       OF THE LABELS MATRIX, AND THE LABELS FOR THE Y-AXIS ARE STORED
C       IN THE SECOND COLUMN.
C
C   2.  ALL PAIRS OF VARIABLES WILL BE PLOTTED ON ONE PAIR OF AXES, SO
C       THE VALUES OF THE VARIABLES SHOULD BE SCALED SIMILARLY (CLUSTER
C       ROUTINE STAND CAN BE USED TO STANDARDIZE THE VARIABLES.) THE
C       OUTPUT IS ON FORTRAN UNIT OUNIT.
C
C   INPUT PARAMETERS
C   ----------------
C
C   NPLOTS INTEGER SCALAR (UNCHANGED ON OUTPUT).
C         THE NUMBER OF PAIRS OF VARIABLES PLOTTED.
C
C   NPTS  INTEGER VECTOR DIMENSIONED AT LEAST NPLOTS (UNCHANGED ON
C            OUTPUT).
C         NPTS(I) IS THE NUMBER OF POINTS TO BE PLOTTED IN THE I-TH PAIR
C           OF VARIABLES.
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C   PTS   REAL MATRIX WHOSE FIRST DIMENSION MUST BE 2 AND SECOND
C            DIMENSION MUST BE AT LEAST SUM(NPTS(I)) FOR I=1,NPLOTS
C            (UNCHANGED ON OUTPUT).
C
C         PTS(1,I) STORES THE X-COORDINATE OF THE I-TH POINT.
C         PTS(2,I) STORES THE Y-COORDINATE OF THE I-TH POINT.
C
C   LABELS MATRIX OF 4-CHARACTER VARIABLES WHOSE FIRST DIMENSION MUST BE
C            2 AND SECOND DIMENSION MUST BE AT LEAST NPLOTS (UNCHANGED
C            ON OUTPUT).
C
C         LABELS(1,I) IS THE LABEL OF THE X-AXIS FOR THE I-TH PAIR OF
C            VARIABLES.
C         LABELS(2,I) IS THE LABEL OF THE Y-AXIS FOR THE I-TH PAIR OF
C            VARIABLES.
C
C   XCHARS VECTOR OF 1-CHARACTER VARIABLES DIMENSIONED AT LEAST NPLOTS
C           (UNCHANGED ON OUTPUT).
C         XCHARS(I) IS THE CHARACTER TO BE PLOTTED FOR THE I-TH PAIR OF
C           VARIABLES.
C
C   OUNIT INTEGER SCALAR (UNCHANGED ON OUTPUT).
C         UNIT NUMBER FOR OUTPUT.
C
C   REFERENCE
C   ---------
C
C     HARTIGAN, J. A. (1975).  CLUSTERING ALGORITHMS, JOHN WILEY &
C        SONS, INC., NEW YORK.  PAGES 39, 45.
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