text: /*
      -- MAGMA (version 2.5.4) --
         Univ. of Tennessee, Knoxville
         Univ. of California, Berkeley
         Univ. of Colorado, Denver
         @date October 2020
  
         @generated from src/zungtr.cpp, normal z -> s, Thu Oct  8 23:05:28 2020
  
  */
  #include "magma_internal.h"
  
  /***************************************************************************//**
      Purpose
      -------
      SORGTR generates a real orthogonal matrix Q which is defined as the
      product of n-1 elementary reflectors of order N, as returned by
      SSYTRD:
  
      if UPLO = MagmaUpper, Q = H(n-1) . . . H(2) H(1),
  
      if UPLO = MagmaLower, Q = H(1) H(2) . . . H(n-1).
  
      Arguments
      ---------
      @param[in]
      uplo    magma_uplo_t
        -     = MagmaUpper: Upper triangle of A contains elementary reflectors
                            from SSYTRD;
        -     = MagmaLower: Lower triangle of A contains elementary reflectors
                            from SSYTRD.
  
      @param[in]
      n       INTEGER
              The order of the matrix Q. N >= 0.
  
      @param[in,out]
      A       REAL array, dimension (LDA,N)
              On entry, the vectors which define the elementary reflectors,
              as returned by SSYTRD.
              On exit, the N-by-N orthogonal matrix Q.
  
      @param[in]
      lda     INTEGER
              The leading dimension of the array A. LDA >= N.
  
      @param[in]
      tau     REAL array, dimension (N-1)
              TAU(i) must contain the scalar factor of the elementary
              reflector H(i), as returned by SSYTRD.
  
      @param[out]
      work    (workspace) REAL array, dimension (LWORK)
              On exit, if INFO = 0, WORK[0] returns the optimal LWORK.
  
      @param[in]
      lwork   INTEGER
              The dimension of the array WORK. LWORK >= N-1.
              For optimum performance LWORK >= N*NB, where NB is
              the optimal blocksize.
      \n
              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.
  
      @param[in]
      dT      REAL array on the GPU device.
              DT contains the T matrices used in blocking the elementary
              reflectors H(i) as returned by magma_ssytrd.
  
      @param[in]
      nb      INTEGER
              This is the block size used in SSYTRD, and correspondingly
              the size of the T matrices, used in the factorization, and
              stored in DT.
  
      @param[out]
      info    INTEGER
        -     = 0:  successful exit
        -     < 0:  if INFO = -i, the i-th argument had an illegal value
  
      @ingroup magma_ungtr
  *******************************************************************************/
  extern "C" magma_int_t
  magma_sorgtr(
      magma_uplo_t uplo, magma_int_t n,
      float *A, magma_int_t lda,
      float *tau,
      float *work, magma_int_t lwork,
      float *dT, magma_int_t nb,
      magma_int_t *info)
  {
  #define A(i,j) (A + (j)*lda+ (i))
  
      magma_int_t i__1;
      magma_int_t i, j;
      magma_int_t iinfo;
      magma_int_t upper, lwkopt, lquery;
  
      *info = 0;
      lquery = (lwork == -1);
      upper = (uplo == MagmaUpper);
      if (! upper && uplo != MagmaLower) {
          *info = -1;
      } else if (n < 0) {
          *info = -2;
      } else if (lda < max(1,n)) {
          *info = -4;
      } else /* if (complicated condition) */ {
          /* Computing MAX */
          if (lwork < max(1, n-1) && ! lquery) {
              *info = -7;
          }
      }
  
      lwkopt = max(1, n) * nb;
      if (*info == 0) {
          work[0] = magma_smake_lwork( lwkopt );
      }
  
      if (*info != 0) {
          magma_xerbla( __func__, -(*info));
          return *info;
      } else if (lquery) {
          return *info;
      }
  
      /* Quick return if possible */
      if (n == 0) {
          work[0] = MAGMA_S_ONE;
          return *info;
      }
  
      if (upper) {
          /*  Q was determined by a call to SSYTRD with UPLO = MagmaUpper
              Shift the vectors which define the elementary reflectors one
              column to the left, and set the last row and column of Q to
              those of the unit matrix                                    */
          for (j = 0; j < n-1; ++j) {
              for (i = 0; i < j-1; ++i)
                  *A(i, j) = *A(i, j + 1);
  
              *A(n-1, j) = MAGMA_S_ZERO;
          }
          for (i = 0; i < n-1; ++i) {
              *A(i, n-1) = MAGMA_S_ZERO;
          }
          *A(n-1, n-1) = MAGMA_S_ONE;
          
          /* Generate Q(1:n-1,1:n-1) */
          i__1 = n - 1;
          lapackf77_sorgql(&i__1, &i__1, &i__1, A(0,0), &lda, tau, work,
                           &lwork, &iinfo);
      } else {
          /*  Q was determined by a call to SSYTRD with UPLO = MagmaLower.
              Shift the vectors which define the elementary reflectors one
              column to the right, and set the first row and column of Q to
              those of the unit matrix                                      */
          for (j = n-1; j > 0; --j) {
              *A(0, j) = MAGMA_S_ZERO;
              for (i = j; i < n-1; ++i)
                  *A(i, j) = *A(i, j - 1);
          }
  
          *A(0, 0) = MAGMA_S_ONE;
          for (i = 1; i < n-1; ++i)
              *A(i, 0) = MAGMA_S_ZERO;
          
          if (n > 1) {
              /* Generate Q(2:n,2:n) */
              magma_sorgqr(n-1, n-1, n-1, A(1, 1), lda, tau, dT, nb, &iinfo);
          }
      }
      
      work[0] = magma_smake_lwork( lwkopt );
  
      return *info;
  } /* magma_sorgtr */
  
  #undef A
  