SGEQP3 (3)  Linux Manuals
NAME
sgeqp3.f 
SYNOPSIS
Functions/Subroutines
subroutine sgeqp3 (M, N, A, LDA, JPVT, TAU, WORK, LWORK, INFO)
SGEQP3
Function/Subroutine Documentation
subroutine sgeqp3 (integerM, integerN, real, dimension( lda, * )A, integerLDA, integer, dimension( * )JPVT, real, dimension( * )TAU, real, dimension( * )WORK, integerLWORK, integerINFO)
SGEQP3
Purpose:

SGEQP3 computes a QR factorization with column pivoting of a matrix A: A*P = Q*R using Level 3 BLAS.
Parameters:

M
M is INTEGER The number of rows of the matrix A. M >= 0.
NN is INTEGER The number of columns of the matrix A. N >= 0.
AA is REAL array, dimension (LDA,N) On entry, the MbyN matrix A. On exit, the upper triangle of the array contains the min(M,N)byN upper trapezoidal matrix R; the elements below the diagonal, together with the array TAU, represent the orthogonal matrix Q as a product of min(M,N) elementary reflectors.
LDALDA is INTEGER The leading dimension of the array A. LDA >= max(1,M).
JPVTJPVT is INTEGER array, dimension (N) On entry, if JPVT(J).ne.0, the Jth column of A is permuted to the front of A*P (a leading column); if JPVT(J)=0, the Jth column of A is a free column. On exit, if JPVT(J)=K, then the Jth column of A*P was the the Kth column of A.
TAUTAU is REAL array, dimension (min(M,N)) The scalar factors of the elementary reflectors.
WORKWORK is REAL array, dimension (MAX(1,LWORK)) On exit, if INFO=0, WORK(1) returns the optimal LWORK.
LWORKLWORK is INTEGER The dimension of the array WORK. LWORK >= 3*N+1. For optimal performance LWORK >= 2*N+( N+1 )*NB, where NB is the optimal blocksize. If LWORK = 1, then a workspace query is assumed; the routine only calculates the optimal size of the WORK array, returns this value as the first entry of the WORK array, and no error message related to LWORK is issued by XERBLA.
INFOINFO is INTEGER = 0: successful exit. < 0: if INFO = i, the ith argument had an illegal value.
Author:

Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
 September 2012
Further Details:

The matrix Q is represented as a product of elementary reflectors Q = H(1) H(2) . . . H(k), where k = min(m,n). Each H(i) has the form H(i) = I  tau * v * v**T where tau is a real scalar, and v is a real/complex vector with v(1:i1) = 0 and v(i) = 1; v(i+1:m) is stored on exit in A(i+1:m,i), and tau in TAU(i).
Contributors:
 G. QuintanaOrti, Depto. de Informatica, Universidad Jaime I, Spain X. Sun, Computer Science Dept., Duke University, USA
Definition at line 152 of file sgeqp3.f.
Author
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