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template<typename T>
void ungqr(integer *m, integer *n, integer *k, T *a, integer *lda, T *tau, T *work, integer *lwork, integer *info)# Form Q from QR factorization.
Purpose:
Generation of an m-by-n complex matrix Q with orthonormal columns, which is defined as the first N columns of a product of K elementary reflectors of order M Q = H(1) H(2) . . . H(k) as returned by SGEQRF.
- Parameters:
m – [in]
m is integer*
The number of rows of the matrix Q. m >= 0.
n – [in]
n is integer*
The number of columns of the matrix Q. m >= n >= 0.
k – [in]
k is integer*
The number of elementary reflectors whose product defines the matrix Q. n >= k >= 0.
a – [inout]
a is COMPLEX/COMPLEX*16 array, dimension (lda,n)
On entry, the i-th column must contain the vector which defines the elementary reflector H(i), for i = 1,2,…,k, as returned by CGEQRF in the first k columns of its array argument a.
On exit, the m-by-n matrix Q.lda – [in]
lda is integer*
The first dimension of the array a. lda >= fla_max(1,m).
tau – [in]
tau is COMPLEX/COMPLEX*16 array, dimension (k)
tau(i) must contain the scalar factor of the elementary reflector H(i), as returned by SGEQRF.
WORK – [out]
WORK is COMPLEX array, dimension (MAX(1,LWORK))
On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
LWORK – [in]
LWORK is INTEGER
The dimension of the array WORK. LWORK >= fla_max(1,N). For optimum performance LWORK >= N*NB, where NB is the optimal blocksize.
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.INFO – [out]
INFO is INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument has an illegal value