Generates the unitary matrix Q of the RQ factorization formed by p?gerqf.


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

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

Include Files


This routine generates the m-by-n complex distributed matrix Q denoting A(ia:ia+m-1,ja:ja+n-1) with orthonormal rows, which is defined as the last m rows of a product of k elementary reflectors of order n

Q = (H(1))H*(H(2))H*...*(H(k))H as returned by p?gerqf.

Input Parameters


(global) INTEGER. The number of rows in the matrix sub(Q); (m0).


(global) INTEGER. The number of columns in the matrix sub(Q) (nm0).


(global) INTEGER. The number of elementary reflectors whose product defines the matrix Q(mk0).



COMPLEX for pcungrq

DOUBLE COMPLEX for pzungrqc

Pointer into the local memory to an array of size (lld_a,LOCc(ja+n-1)). The i-th row must contain the vector that defines the elementary reflector H(i), ia+m-kiia+m-1, as returned by p?gerqf in the k rows of its distributed matrix argument A(ia+m-k:ia+m-1, ja:*).

ia, ja

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


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



COMPLEX for pcungrq

DOUBLE COMPLEX for pzungrq

Array of size LOCr(ia+m-1).

Contains the scalar factor tau(i) of elementary reflectors H(i) as returned by p?gerqf. tau is tied to the distributed matrix A.



COMPLEX for pcungrq

DOUBLE COMPLEX for pzungrq

Workspace array of size of lwork.


(local or global) INTEGER, size of work, must be at least lworkmb_a*(mpa0 +nqa0+mb_a), where

iroffa = mod(ia-1, mb_a),

icoffa = mod(ja-1, nb_a),

iarow = indxg2p(ia, mb_a, MYROW, rsrc_a, NPROW),

iacol = indxg2p(ja, nb_a, MYCOL, csrc_a, NPCOL),

mpa0 = numroc(m+iroffa, mb_a, MYROW, iarow, NPROW),

nqa0 = numroc(n+icoffa, nb_a, MYCOL, iacol, NPCOL)


mod(x,y) is the integer remainder of x/y.

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


Contains the local pieces of the m-by-n distributed matrix Q.


On exit work(1) contains the minimum value of lwork required for optimum performance.


(global) INTEGER.

= 0: the execution is successful.

< 0: if the i-th argument is an array and the j-th 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.

See Also

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