Computes a QR factorization of a general rectangular matrix (unblocked algorithm).
void psgeqr2 (MKL_INT *m , MKL_INT *n , float *a , MKL_INT *ia , MKL_INT *ja , MKL_INT *desca , float *tau , float *work , MKL_INT *lwork , MKL_INT *info );
void pdgeqr2 (MKL_INT *m , MKL_INT *n , double *a , MKL_INT *ia , MKL_INT *ja , MKL_INT *desca , double *tau , double *work , MKL_INT *lwork , MKL_INT *info );
void pcgeqr2 (MKL_INT *m , MKL_INT *n , MKL_Complex8 *a , MKL_INT *ia , MKL_INT *ja , MKL_INT *desca , MKL_Complex8 *tau , MKL_Complex8 *work , MKL_INT *lwork , MKL_INT *info );
void pzgeqr2 (MKL_INT *m , MKL_INT *n , MKL_Complex16 *a , MKL_INT *ia , MKL_INT *ja , MKL_INT *desca , MKL_Complex16 *tau , MKL_Complex16 *work , MKL_INT *lwork , MKL_INT *info );
The p?geqr2function computes a QR factorization of a real/complex distributed m-by-n matrix sub(A) = A(ia:ia+m-1, ja:ja+n-1)= Q*R.
The number of rows in the distributed matrix sub(A). (m≥0).
(global) The number of columns in the distributed matrix sub(A). (n≥0).
Pointer into the local memory to an array of size lld_a * LOCc(ja+n-1).
On entry, this array contains the local pieces of the m-by-n distributed matrix sub(A) which is to be factored.
- ia, ja
(global) The row and column indices in the global matrix A indicating the first row and the first column of sub(A), respectively.
(global and local) array of size dlen_. The array descriptor for the distributed matrix A.
This is a workspace array of size lwork.
(local or global)
The size of the array work.
lwork is local input and must be at least lwork≥mp0+max(1, nq0),
where iroff = mod(ia-1, mb_a), icoff = mod(ja-1, nb_a),
iarow = indxg2p(ia, mb_a, myrow, rsrc_a, nprow),
iacol = indxg2p(ja, nb_a, mycol, csrc_a, npcol),
mp0 = numroc(m+iroff, mb_a, myrow, iarow, nprow),
nq0 = numroc(n+icoff, nb_a, mycol, iacol, npcol).
indxg2p and numroc are ScaLAPACK tool functions; myrow, mycol, nprow, and npcol can be determined by calling the function blacs_gridinfo.
If lwork = -1, then lwork is global input and a workspace query is assumed; the function only calculates the minimum and optimal size for all work arrays. Each of these values is returned in the first entry of the corresponding work array, and no error message is issued by pxerbla.
On exit, the elements on and above the diagonal of sub(A) contain the min(m,n) by n upper trapezoidal matrix R (R is upper triangular if m≥n); the elements below the diagonal, with the array tau, represent the orthogonal/unitary matrix Q as a product of elementary reflectors (see Application Notes below).
Array of size LOCc(ja+min(m,n)-1). This array contains the scalar factors of the elementary reflectors. tau is tied to the distributed matrix A.
On exit, work returns the minimal and optimal lwork.
If info = 0, the execution is successful. if info < 0:
If the i-th argument is an array and the j-th entry, indexed j-1, had an illegal value, then info = - (i*100+j),
if the i-th argument is a scalar and had an illegal value, then info = -i.
The matrix Q is represented as a product of elementary reflectors
Q = H(ja)*H(ja+1)*. . .* H(ja+k-1), where k = min(m,n).
Each H(i) has the form
H(j)= I - tau*v*v',
where tau is a real/complex scalar, and v is a real/complex vector with v(1: i-1) = 0 and v(i) = 1; v(i+1: m) is stored on exit in A(ia+i:ia+m-1, ja+i-1), and tau in tau[ja+i-2].