SUBROUTINE POLYFT(X,Y,SIG,N,ORDER,A,YFIT,ISTAT)
*
*  Module number: HRS/FOS utility
*
*  Module name: polyft
*
*  Keyphrase:
*  ----------
*       least squares polynomial fit
*
*  Description:
*  ------------
*       This routine does a least squares polynomial fit
*       to input data y versus x.  The Numerical recipe
*       routine LFIT is used to minimize chi squared.
*
*  FORTRAN name: polyft.for
*
*  Keywords of accessed files and tables:
*  --------------------------------------
*       none
*
*  Subroutines Called:
*  -------------------
*  SDAS:
*       umsput
*  Others:
*       LFIT
*
*  History:
*  --------
*  Version      Date        Author          Description
*     1       Oct. 87     D. Lindler      Designed and coded
*-------------------------------------------------------------------------------
C
C INPUT PARAMETERS
C
C       X - X VECTOR (REAL*8)
C       Y - Y VECTOR (REAL*8)
C       SIG - STANDARD DEVIATION VECTOR FOR Y (REAL*8)
C       N - NUMBER OF POINTS IN X AND Y
C       ORDER - ORDER OF THE POLYNOMIAL (INTEGER)
C
C OUTPUT PARAMETERS
C
C       A - FITTED POLYNOMIAL COEFFICIENTS (REAL*8)
C       YFIT - VECTOR OF FITTED VALUES (REAL*8)
C       ISTAT - ERROR STATUS (INTEGER)
C------------------------------------------------------------------------------
C     INCLUDE FILE FOR THE IRAF77 FORTRAN INTERFACE TO THE IRAF VOS
C
C
C     FILE I/O ACCESS MODES
C
      INTEGER   RDONLY
      PARAMETER (RDONLY = 1)
      INTEGER   RDWRIT
      PARAMETER (RDWRIT = 2)
      INTEGER   WRONLY
      PARAMETER (WRONLY = 3)
      INTEGER   APPEND
      PARAMETER (APPEND = 4)
C
C     CODES FOR DATA TYPES
C
      INTEGER   TYBOOL
      PARAMETER (TYBOOL = 1)
      INTEGER   TYCHAR
      PARAMETER (TYCHAR = 2)
      INTEGER   TYINT
      PARAMETER (TYINT = 4)
      INTEGER   TYREAL
      PARAMETER (TYREAL = 6)
      INTEGER   TYDOUB
      PARAMETER (TYDOUB = 7)
C
C     UMSPUT DESTINATIONS -- CB, DAO, 4-SEP-87
C
      INTEGER STDOUT
      PARAMETER (STDOUT = 1)
      INTEGER STDERR
      PARAMETER (STDERR = 2)
C
C     UHDAS HEADER PARM TYPES -- CB, DAO, 5-SEP-87
C
      INTEGER GENHDR
      PARAMETER (GENHDR = 0)
      INTEGER IMSPEC
      PARAMETER (IMSPEC = 1)
C
C     THIS SECTION IS FOR PARAMETERS RELEVANT TO TABLE I/O.
C
C     THESE MAY BE SET BY UTPPTI AND/OR READ BY UTPGTI:
C
C                                       LENGTH OF ROW (UNIT = SIZE OF REAL)
      INTEGER   TBRLEN
      PARAMETER (TBRLEN = 1)
C                                       INCREASE ROW LENGTH
      INTEGER   TBIRLN
      PARAMETER (TBIRLN = 2)
C                                       NUMBER OF ROWS TO ALLOCATE
      INTEGER   TBALLR
      PARAMETER (TBALLR = 3)
C                                       INCREASE ALLOC NUM OF ROWS
      INTEGER   TBIALR
      PARAMETER (TBIALR = 4)
C                                       WHICH TYPE OF TABLE? (ROW OR COLUMN)
      INTEGER   TBWTYP
      PARAMETER (TBWTYP = 5)
C                                       MAXIMUM NUMBER OF USER PARAMETERS
      INTEGER   TBMXPR
      PARAMETER (TBMXPR = 6)
C                                       MAXIMUM NUMBER OF COLUMNS
      INTEGER   TBMXCL
      PARAMETER (TBMXCL = 7)
C                                       TYPE = ROW-ORDERED TABLE
      INTEGER   TBTYPR
      PARAMETER (TBTYPR = 11)
C                                       TYPE = COLUMN-ORDERED TABLE
      INTEGER   TBTYPC
      PARAMETER (TBTYPC = 12)
C
C     THESE MAY BE READ BY UTPGTI BUT MAY NOT BE SET:
C
C                                       NUMBER OF ROWS WRITTEN TO
      INTEGER   TBNROW
      PARAMETER (TBNROW = 21)
C
C     END IRAF77.INC
        DOUBLE PRECISION X(1),Y(1),SIG(1),A(1),YFIT(1)
        INTEGER N,ORDER,ISTAT
C
C LOCAL VARIABLES
C
        DOUBLE PRECISION COVAR(10,10),CHISQ
        INTEGER LISTA(10)
        INTEGER I,J
C
C  DATA DECLARATIONS
C
        EXTERNAL POLY1
        DATA LISTA/1,2,3,4,5,6,7,8,9,10/
C
C CHECK INPUT PARAMETERS FOR VALIDITY
C
        ISTAT=0
        IF (ORDER.GT.(N-1))THEN
                CALL UMSPUT('Too few points to perform polynomial fit',
     *                  STDERR+STDOUT,0,ISTAT)
                ISTAT=1
                GO TO 999
        ENDIF
        IF(ORDER.GT.9)THEN
                CALL UMSPUT('Maximum order of polynomial is 9',
     *                  STDERR+STDOUT,0,ISTAT)
                ISTAT=1
                GO TO 999
        ENDIF
C
C PERFORM FIT
C
        CALL LFIT(X,Y,SIG,N,A,ORDER+1,LISTA,ORDER+1,COVAR,
     *          10,CHISQ,POLY1,ISTAT)
        IF(ISTAT.NE.0)THEN
                CALL UMSPUT('Unable to perform polynomial fit',
     *                  STDERR+STDOUT,0,ISTAT)
                ISTAT=1
                GO TO 999
        ENDIF
C
C COMPUTE YFIT
C
        DO 10 I=1,N
                YFIT(I)=A(1)
                IF(ORDER.GT.0) THEN
                        DO 5 J=1,ORDER
                                YFIT(I)=YFIT(I)+A(J+1)*X(I)**J
5                       CONTINUE
                ENDIF
10      CONTINUE
        ISTAT=0
999     RETURN
        END