p?geql2

Computes a QL factorization of a general rectangular matrix (unblocked algorithm).

Syntax

Fortran:

call psgeql2(m, n, a, ia, ja, desca, tau, work, lwork, info)

call pdgeql2(m, n, a, ia, ja, desca, tau, work, lwork, info)

call pcgeql2(m, n, a, ia, ja, desca, tau, work, lwork, info)

call pzgeql2(m, n, a, ia, ja, desca, tau, work, lwork, info)

C:

void psgeql2 (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 pdgeql2 (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 pcgeql2 (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 pzgeql2 (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 );

Include Files

  • C: mkl_scalapack.h

Description

The p?geql2 routine computes a QL factorization of a real/complex distributed m-by-n matrix sub(A) = A(ia:ia+m-1, ja:ja+n-1)= Q *L.

Input Parameters

m

(global) INTEGER.

The number of rows to be operated on, that is, the number of rows of the distributed submatrix sub(A). (m 0).

n

(global) INTEGER.

The number of columns to be operated on, that is, the number of columns of the distributed submatrix sub(A). (n 0).

a

(local).

REAL for psgeql2

DOUBLE PRECISION for pdgeql2

COMPLEX for pcgeql2

COMPLEX*16 for pzgeql2.

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) INTEGER. The row and column indices in the global array a indicating the first row and the first column of the submatrix A, respectively.

desca

(global and local) INTEGER array, size (dlen_). The array descriptor for the distributed matrix A.

work

(local).

REAL for psgeql2

DOUBLE PRECISION for pdgeql2

COMPLEX for pcgeql2

COMPLEX*16 for pzgeql2.

This is a workspace array of size (lwork).

lwork

(local or global) INTEGER.

The size of the array work.

lwork is local input and must be at least lworkmp0 + 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 subroutine blacs_gridinfo.

If lwork = -1, then lwork is global input and a workspace query is assumed; the routine 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.

Output Parameters

a

(local).

On exit,

if m n, the lower triangle of the distributed submatrix A(ia+m-n:ia+m-1, ja:ja+n-1) contains the n-by-n lower triangular matrix L;

if mn, the elements on and below the (n-m)-th superdiagonal contain the m-by-n lower trapezoidal matrix L; the remaining elements, with the array tau, represent the orthogonal/ unitary matrix Q as a product of elementary reflectors (see Application Notes below).

tau

(local).

REAL for psgeql2

DOUBLE PRECISION for pdgeql2

COMPLEX for pcgeql2

COMPLEX*16 for pzgeql2.

Array, size LOCc(ja+n-1). This array contains the scalar factors of the elementary reflectors. tau is tied to the distributed matrix A.

work

On exit, work(1) returns the minimal and optimal lwork.

info

(local). INTEGER.

If info = 0, the execution is successful. if info < 0: If the i-th argument is an array and the j-entry 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.

Application Notes

The matrix Q is represented as a product of elementary reflectors

Q = H(ja+k-1)*...*H(ja+1)*H(ja), where k = min(m,n).

Each H(i) has the form

H(i) = I- tau *v*v'

where tau is a real/complex scalar, and v is a real/complex vector with v(m-k+i+1: m) = 0 and v(m-k+i) = 1; v(1: m-k+i-1) is stored on exit in A(ia:ia+m-k+i-2, ja+n-k+i-1), and tau in TAU(ja+n-k+i-1).

For more complete information about compiler optimizations, see our Optimization Notice.