NAME

SYNOPSIS

  SUBROUTINE DQRDC( A, LDA, N, P, QRAUX, IPIVOT, WORK, JOB)
  INTEGER LDA, N, P, JOB
  INTEGER IPIVOT(*)
  DOUBLE PRECISION A(LDA,*), QRAUX(*), WORK(*)
 
  SUBROUTINE DQRDC_64( A, LDA, N, P, QRAUX, IPIVOT, WORK, JOB)
  INTEGER*8 LDA, N, P, JOB
  INTEGER*8 IPIVOT(*)
  DOUBLE PRECISION A(LDA,*), QRAUX(*), WORK(*)
 

C INTERFACE

void dqrdc(double *a, int lda, int n, int p, double *qraux, int *ipivot, int job);

void dqrdc_64(double *a, long lda, long n, long p, double *qraux, long *ipivot, long job);

ARGUMENTS

* A (input/output)

On entry, the matrix A. On exit, the upper triangle 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 (input)

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

* N (input)

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

* P (input)

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

* QRAUX (output)

On exit, contains information required to construct the orthogonal matrix Q.

* IPIVOT (input)

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 selection 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 initial elements to the beginning of A and final elements 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) contains the index of the diagonal element of A that was moved into the kth position.

* WORK (workspace)

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

* JOB (input)

Determines how the factorization is done:

• 0 with no pivoting

        not 0   with pivoting