LAPACK
3.4.2
LAPACK: Linear Algebra PACKage

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Functions/Subroutines  
subroutine  dlaqps (M, N, OFFSET, NB, KB, A, LDA, JPVT, TAU, VN1, VN2, AUXV, F, LDF) 
DLAQPS computes a step of QR factorization with column pivoting of a real mbyn matrix A by using BLAS level 3. 
subroutine dlaqps  (  integer  M, 
integer  N,  
integer  OFFSET,  
integer  NB,  
integer  KB,  
double precision, dimension( lda, * )  A,  
integer  LDA,  
integer, dimension( * )  JPVT,  
double precision, dimension( * )  TAU,  
double precision, dimension( * )  VN1,  
double precision, dimension( * )  VN2,  
double precision, dimension( * )  AUXV,  
double precision, dimension( ldf, * )  F,  
integer  LDF  
) 
DLAQPS computes a step of QR factorization with column pivoting of a real mbyn matrix A by using BLAS level 3.
Download DLAQPS + dependencies [TGZ] [ZIP] [TXT]DLAQPS computes a step of QR factorization with column pivoting of a real MbyN matrix A by using Blas3. It tries to factorize NB columns from A starting from the row OFFSET+1, and updates all of the matrix with Blas3 xGEMM. In some cases, due to catastrophic cancellations, it cannot factorize NB columns. Hence, the actual number of factorized columns is returned in KB. Block A(1:OFFSET,1:N) is accordingly pivoted, but not factorized.
[in]  M  M is INTEGER The number of rows of the matrix A. M >= 0. 
[in]  N  N is INTEGER The number of columns of the matrix A. N >= 0 
[in]  OFFSET  OFFSET is INTEGER The number of rows of A that have been factorized in previous steps. 
[in]  NB  NB is INTEGER The number of columns to factorize. 
[out]  KB  KB is INTEGER The number of columns actually factorized. 
[in,out]  A  A is DOUBLE PRECISION array, dimension (LDA,N) On entry, the MbyN matrix A. On exit, block A(OFFSET+1:M,1:KB) is the triangular factor obtained and block A(1:OFFSET,1:N) has been accordingly pivoted, but no factorized. The rest of the matrix, block A(OFFSET+1:M,KB+1:N) has been updated. 
[in]  LDA  LDA is INTEGER The leading dimension of the array A. LDA >= max(1,M). 
[in,out]  JPVT  JPVT is INTEGER array, dimension (N) JPVT(I) = K <==> Column K of the full matrix A has been permuted into position I in AP. 
[out]  TAU  TAU is DOUBLE PRECISION array, dimension (KB) The scalar factors of the elementary reflectors. 
[in,out]  VN1  VN1 is DOUBLE PRECISION array, dimension (N) The vector with the partial column norms. 
[in,out]  VN2  VN2 is DOUBLE PRECISION array, dimension (N) The vector with the exact column norms. 
[in,out]  AUXV  AUXV is DOUBLE PRECISION array, dimension (NB) Auxiliar vector. 
[in,out]  F  F is DOUBLE PRECISION array, dimension (LDF,NB) Matrix F**T = L*Y**T*A. 
[in]  LDF  LDF is INTEGER The leading dimension of the array F. LDF >= max(1,N). 
Definition at line 177 of file dlaqps.f.