C 
      SUBROUTINE TTSORT(NQ,NPTS,ITIME,OUT,IRECS,RECS,INDX)
      INTEGER NQ,NPTS,ITIME,IRECS(NPTS),INDX(NPTS)
      REAL OUT(NQ,NPTS),RECS(NPTS)
C
C Subroutine designed to sort two-point rays according to receiver
C indices.  For the same receiver, the rays are sorted according to
C travel time.
C
C Input:
C     NQ...   Number of real quantities considered at a ray point.
C             If NQ is less than ITIME, no subsequent sorting according
C             to travel time is performed.
C     NPTS... Number of ray points stored in array OUT.
C     ITIME...Rays at each receiver are sorted according to travel times
C             OUT(ITIME,*).
C     OUT...  For each ray point, NQ quantities, the ITIME-th of them
C             should be travel time.
C     IRECS.. Indices of receivers corresponding to rays.
C     RECS... Temporary storage array for floating-point counterpart of
C             integer array IRECS.  May be equivalent with IRECS, i.e.
C             may be declared by statements
C               REAL RECS(NPTS)
C               EQUIVALENCE (IRECS,RECS)
C             in the calling subroutine.
C Output:
C     INDX... Indices of sorted rays.
C
C Subroutines and external functions required:
      EXTERNAL INDEXX
C     INDEXX..File 'indexx.for'.
C
C Date: 1996, September 30
C Coded by Ludek Klimes
C
C-----------------------------------------------------------------------
C
C     Local storage locations:
      INTEGER I,I1,J,JREC
      REAL TTMIN,TTSCL
C
C.......................................................................
C
C     Sorting according to (1) receivers, (2) travel times:
      IF (NQ.GE.ITIME) THEN
        TTMIN= 999999.
        TTSCL=-999999.
        DO 11 I=1,NPTS
          TTMIN=AMIN1(OUT(ITIME,I),TTMIN)
          TTSCL=AMAX1(OUT(ITIME,I),TTSCL)
   11   CONTINUE
        TTSCL=TTSCL-TTMIN
        IF(TTSCL.GT.0.) THEN
          TTSCL=0.998/TTSCL
        END IF
        DO 12 I=1,NPTS
          RECS(I)=FLOAT(IRECS(I))+0.001+(OUT(ITIME,I)-TTMIN)*TTSCL
   12   CONTINUE
      ELSE
        DO 13 I=1,NPTS
          RECS(I)=FLOAT(IRECS(I))+0.001
   13   CONTINUE
      END IF
      CALL INDEXX(NPTS,RECS,INDX)
      DO 14 I=1,NPTS
        IRECS(I)=INT(RECS(I))
   14 CONTINUE
C
C     Fine resorting according to travel times:
      IF (NQ.GE.ITIME) THEN
        I1=1
   21   CONTINUE
        JREC=0
        DO 22 I=I1,NPTS
          J=INDX(I)
          IF(IRECS(J).EQ.JREC) THEN
            IF(OUT(ITIME,J).LT.OUT(ITIME,INDX(I-1))) THEN
C             Exchanging rays, and checking the receiver again:
              INDX(I)  =INDX(I-1)
              INDX(I-1)=J
              GO TO 21
            END IF
          ELSE
            I1=I
          END IF
          JREC=IRECS(J)
   22   CONTINUE
      END IF
C
      RETURN
      END
C
C=======================================================================
C