ZUNGTR generates a complex unitary matrix Q which is defined as the


 product of n-1 elementary reflectors of order N, as returned by


 ZHETRD:


 if UPLO = 'U', Q = H(n-1) . . . H(2) H(1),


 if UPLO = 'L', Q = H(1) H(2) . . . H(n-1).

UPLO

          UPLO is CHARACTER*1


          = 'U': Upper triangle of A contains elementary reflectors


                 from ZHETRD;


          = 'L': Lower triangle of A contains elementary reflectors


                 from ZHETRD.

N

          N is INTEGER


          The order of the matrix Q. N >= 0.

A

          A is COMPLEX*16 array, dimension (LDA,N)


          On entry, the vectors which define the elementary reflectors,


          as returned by ZHETRD.


          On exit, the N-by-N unitary matrix Q.

LDA

          LDA is INTEGER


          The leading dimension of the array A. LDA >= N.

TAU

          TAU is COMPLEX*16 array, dimension (N-1)


          TAU(i) must contain the scalar factor of the elementary


          reflector H(i), as returned by ZHETRD.

WORK

          WORK is COMPLEX*16 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 >= N-1.


          For optimum performance LWORK >= (N-1)*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

Univ. of Tennessee

Univ. of California Berkeley

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NAG Ltd.

November 2011