?unmqr

Developer Reference for Intel® oneAPI Math Kernel Library for Fortran

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ID 766686

Date 12/16/2022

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?unmqr

Multiplies a complex matrix by the unitary matrix Q of the QR factorization formed by ?geqrf.

Syntax

call cunmqr(side, trans, m, n, k, a, lda, tau, c, ldc, work, lwork, info)

call zunmqr(side, trans, m, n, k, a, lda, tau, c, ldc, work, lwork, info)

call unmqr(a, tau, c [,side] [,trans] [,info])

Include Files

mkl.fi, lapack.f90

Description

The routine multiplies a rectangular complex matrix C by Q or Q^H, where Q is the unitary matrix Q of the QR factorization formed by the routines ?geqrf or geqpf.

Depending on the parameters side and trans, the routine can form one of the matrix products Q*C, Q^H*C, C*Q, or C*Q^H (overwriting the result on C).

Input Parameters

side

CHARACTER*1. Must be either 'L' or 'R'.

If side = 'L', Q or Q^H is applied to C from the left.

If side = 'R', Q or Q^H is applied to C from the right.

trans

CHARACTER*1. Must be either 'N' or 'C'.

If trans = 'N', the routine multiplies C by Q.

If trans = 'C', the routine multiplies C by Q^H.

m

INTEGER. The number of rows in the matrix C (m≥ 0).

n

INTEGER. The number of columns in C (n≥ 0).

k

INTEGER. The number of elementary reflectors whose product defines the matrix Q. Constraints:

0 ≤k≤m if side = 'L';

0 ≤k≤n if side = 'R'.

a, c, tau, work

COMPLEX for cgeqrf

DOUBLE COMPLEX for zgeqrf.

Arrays:

a(lda,*) and tau(*) are the arrays returned by cgeqrf / zgeqrf or cgeqpf / zgeqpf.

The second dimension of a must be at least max(1, k).

The size of tau must be at least max(1, k).

c(ldc,*) contains the m-by-n matrix C.

The second dimension of c must be at least max(1, n)

work is a workspace array, its dimension max(1, lwork).

lda

INTEGER. The leading dimension of a. Constraints:

lda≥ max(1, m) if side = 'L';

lda≥ max(1, n) if side = 'R'.

ldc

INTEGER. The leading dimension of c. Constraint:

ldc≥ max(1, m) .

lwork

INTEGER. The size of the work array. Constraints:

lwork≥ max(1, n) if side = 'L';

lwork≥ max(1, m) if side = 'R'.

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.

See Application notes for the suggested value of lwork.

Output Parameters

c

Overwritten by the product Q*C, Q^H*C, C*Q, or C*Q^H (as specified by side and trans).

work(1)

If info = 0, on exit work(1) contains the minimum value of lwork required for optimum performance. Use this lwork for subsequent runs.

info

INTEGER.

If info = 0, the execution is successful.

If info = -i, the i-th parameter had an illegal value.

LAPACK 95 Interface Notes

Routines in Fortran 95 interface have fewer arguments in the calling sequence than their FORTRAN 77 counterparts. For general conventions applied to skip redundant or restorable arguments, see LAPACK 95 Interface Conventions.

Specific details for the routine unmqr interface are the following:

a

Holds the matrix A of size (r,k).

r = m if side = 'L'.

r = n if side = 'R'.

tau

Holds the vector of length (k).

c

Holds the matrix C of size (m,n).

side

Must be 'L' or 'R'. The default value is 'L'.

trans

Must be 'N' or 'C'. The default value is 'N'.

Application Notes

For better performance, try using lwork = n*blocksize (if side = 'L') or lwork = m*blocksize (if side = 'R') where blocksize is a machine-dependent value (typically, 16 to 64) required for optimum performance of the blocked algorithm.

If it is not clear how much workspace to supply, use a generous value of lwork for the first run, or set lwork = -1.

In first case the routine completes the task, though probably not so fast as with a recommended workspace, and provides the recommended workspace in the first element of the corresponding array work on exit. Use this value (work(1)) for subsequent runs.

If lwork = -1, then the routine returns immediately and provides the recommended workspace in the first element of the corresponding array (work). This operation is called a workspace query.

Note that if lwork is less than the minimal required value and is not equal to -1, then the routine returns immediately with an error exit and does not provide any information on the recommended workspace.

The real counterpart of this routine is ormqr.

Parent topic: Orthogonal Factorizations: LAPACK Computational Routines

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?unmqr