# cunghr.f man page

cunghr.f

## Synopsis

### Functions/Subroutines

subroutine **cunghr** (**N**, ILO, IHI, A, **LDA**, TAU, WORK, LWORK, INFO)**CUNGHR**

## Function/Subroutine Documentation

### subroutine cunghr (integer N, integer ILO, integer IHI, complex, dimension( lda, * ) A, integer LDA, complex, dimension( * ) TAU, complex, dimension( * ) WORK, integer LWORK, integer INFO)

**CUNGHR**

**Purpose:**

CUNGHR generates a complex unitary matrix Q which is defined as the product of IHI-ILO elementary reflectors of order N, as returned by CGEHRD: Q = H(ilo) H(ilo+1) . . . H(ihi-1).

**Parameters:**-
*N*N is INTEGER The order of the matrix Q. N >= 0.

*ILO*ILO is INTEGER

*IHI*IHI is INTEGER ILO and IHI must have the same values as in the previous call of CGEHRD. Q is equal to the unit matrix except in the submatrix Q(ilo+1:ihi,ilo+1:ihi). 1 <= ILO <= IHI <= N, if N > 0; ILO=1 and IHI=0, if N=0.

*A*A is COMPLEX array, dimension (LDA,N) On entry, the vectors which define the elementary reflectors, as returned by CGEHRD. On exit, the N-by-N unitary matrix Q.

*LDA*LDA is INTEGER The leading dimension of the array A. LDA >= max(1,N).

*TAU*TAU is COMPLEX array, dimension (N-1) TAU(i) must contain the scalar factor of the elementary reflector H(i), as returned by CGEHRD.

*WORK*WORK is COMPLEX array, dimension (MAX(1,LWORK)) On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

*LWORK*LWORK is INTEGER The dimension of the array WORK. LWORK >= IHI-ILO. For optimum performance LWORK >= (IHI-ILO)*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*INFO is INTEGER = 0: successful exit < 0: if INFO = -i, the i-th argument had an illegal value

**Author:**-
Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date:**December 2016

Definition at line 128 of file cunghr.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page cunghr(3) is an alias of cunghr.f(3).

Tue Nov 14 2017 Version 3.8.0 LAPACK