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NAME
     zqrdc - compute the QR factorization of a general matrix  A.
     It  is  typical  to  follow  a  call to xQRDC with a call to
     xQRSL to solve Ax = b or to xPODI to compute the determinant
     of A.

SYNOPSIS
     SUBROUTINE DQRDC (DA, LDA, N, P, DQRAUX, IPIVOT, DWORK, JOB)

     SUBROUTINE SQRDC (SA, LDA, N, P, SQRAUX, IPIVOT, SWORK, JOB)

     SUBROUTINE ZQRDC (ZA, LDA, N, P, ZQRAUX, IPIVOT, ZWORK, JOB)

     SUBROUTINE CQRDC (CA, LDA, N, P, CQRAUX, IPIVOT, CWORK, JOB)



     #include <sunperf.h>

     void dqrdc(double *dx, int ldx, int n, int p, double *qraux,
               int *jpivot, int job) ;

     void sqrdc(float *sx, int ldx, int n, int p,  float  *qraux,
               int *jpivot, int job) ;

     void zqrdc(doublecomplex *zx, int ldx, int n, int  p,  doub-
               lecomplex *qraux, int *jpivot, int job) ;

     void cqrdc(complex *cx, int  ldx,  int  n,  int  p,  complex
               *qraux, int *jpivot, int job) ;

ARGUMENTS
     xA        On entry, the matrix A.  On exit, the upper trian-
               gle  of  A  contains  the  matrix R and the strict
               lower triangle of A contains information that will
               allow  construction  of the matrix Q.  If pivoting
               was requested, A contains the factorization of the
               original   matrix  A  permuted  by  the  requested
               pivots.

     LDA       Leading dimension of the array A as specified in a
               dimension or type statement.  LDA >= max(1,N).

     N         Number of rows in the matrix A.  N >= 0.

     P         Number of columns in the matrix A.  P >= 0.

     xQRAUX    On exit, contains  information  required  to  con-
               struct the orthogonal matrix Q.

     IPIVOT    If JOB selected no pivoting, then  IPIVOT  is  not
               referenced.   If  JOB  selected  pivoting, then on
               entry to the subroutines, IPIVOT contains integers
               representing array indices that control the selec-
               tion of pivot elements  from  the  diagonal  of  A
               according to the system below:
                    IPIVOT(k) > 0  A(k,k) is an initial element.
                    IPIVOT(k) = 0  A(k,k) is a free element.
                    IPIVOT(k) < 0  A(k,k) is a final element.
               Before the decomposition  is  computed,  symmetric
               row  and column interchanges are used to move ini-
               tial elements to the beginning of A and final ele-
               ments  to  the  end of A.  During the computation,
               symmetric row and column interchanges are used  to
               move  the  largest remaining free diagonal element
               into the pivot position.  On exit, IPIVOT(k)  con-
               tains  the index of the diagonal element of A that
               was moved into the kth position.

     xWORK     Scratch array with a dimension of N.  WORK is  not
               referenced if JOB = 0.

     JOB       Determines how the factorization is done:
                    0    with no pivoting
                    not 0     with pivoting

SAMPLE PROGRAM
           PROGRAM TEST
           IMPLICIT NONE
     C
           INTEGER           IDOB, IDORSD, IDOXB, LDA, N, NCOLA, NOPIV, NROWA
           PARAMETER        (IDOB = 100)
           PARAMETER        (IDORSD = 10)
           PARAMETER        (IDOXB = 1)
           PARAMETER        (N = 3)
           PARAMETER        (LDA = N)
           PARAMETER        (NCOLA = 2)
           PARAMETER        (NOPIV = 0)
           PARAMETER        (NROWA = N)
     C
           DOUBLE PRECISION  A(LDA,NCOLA), B(NCOLA), NULL(N), QRAUX(N)
           DOUBLE PRECISION  RESID(N), WORK(N), Y(N)
           INTEGER           ICOL, INFO, IROW, JOB, JPIVOT
     C
           EXTERNAL          DQRDC, DQRSL
     C
     C      Initialize the array A to store the matrix A shown below.
     C      Initialize the array Y to store the vector y shown below.
     C
     C          1  1         1
     C      A = 1  0    y =  0
     C          0  1        -5
     C
           DATA A / 1.0D0, 1.0D0, 0.0D0, 1.0D0, 0.0D0, 1.0D0 /
           DATA Y / 1.0D0, 0.0D0, -5.0D0 /
     C
           PRINT 1000
           PRINT 1010, ((A(IROW,ICOL), ICOL = 1, NCOLA), IROW = 1, NROWA)
           PRINT 1020
           PRINT 1030, Y
           JOB = NOPIV
           CALL DQRDC (A, LDA, NROWA, NCOLA, QRAUX, JPIVOT, WORK, JOB)
           JOB = IDOB + IDORSD + IDOXB
           CALL DQRSL (A, LDA, NROWA, NCOLA, QRAUX, Y, NULL, NULL, B,
          $            RESID, NULL, JOB, INFO)
           IF (INFO .EQ. 0) THEN
             PRINT 1040
             PRINT 1050, B
             PRINT 1060
             PRINT 1050, RESID
           ELSE
             PRINT 1070
           END IF
     C
      1000 FORMAT (1X, 'A:')
      1010 FORMAT (2(3X, F4.1))
      1020 FORMAT (/1X, 'y:')
      1030 FORMAT (3X, F4.1)
      1040 FORMAT (/1X, 'Least squares solution:')
      1050 FORMAT (3X, F4.1)
      1060 FORMAT (/1X, 'Residual:')
      1070 FORMAT (1X, 'A is singular.')
     C
           END

SAMPLE OUTPUT
      A:
         1.0    1.0
         1.0    0.0
         0.0    1.0

      y:
         1.0
         0.0
        -5.0

      Least squares solution:
         2.0
        -3.0

      Residual:
         2.0
        -2.0
        -2.0

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