extern "C" void
magma_dlarfxsym(
magma_int_t N,
double *A, magma_int_t LDA,
double *V, double *TAU)
{
magma_int_t IONE=1;
double dtmp;
double Z_ZERO = MAGMA_D_ZERO;
//double Z_ONE = MAGMA_D_ONE;
double Z_MONE = MAGMA_D_NEG_ONE;
double Z_HALF = MAGMA_D_HALF;
//double WORK[N];
double *WORK;
magma_dmalloc_cpu( &WORK, N );
/* apply left and right on A(st:ed,st:ed)*/
//magma_dlarfxsym(len,A(st,st),LDX,V(st),TAU(st));
/* X = AVtau */
blasf77_dsymv("L",&N, TAU, A, &LDA, V, &IONE, &Z_ZERO, WORK, &IONE);
/* je calcul dtmp= X'*V */
dtmp = magma_cblas_ddot(N, WORK, IONE, V, IONE);
/* je calcul 1/2 X'*V*t = 1/2*dtmp*tau */
dtmp = -dtmp * Z_HALF * (*TAU);
/* je calcul W=X-1/2VX'Vt = X - dtmp*V */
/*
for (j = 0; j < N; j++)
WORK[j] = WORK[j] + (dtmp*V[j]); */
blasf77_daxpy(&N, &dtmp, V, &IONE, WORK, &IONE);
/* performs the symmetric rank 2 operation A := alpha*x*y' + alpha*y*x' + A */
blasf77_dsyr2("L",&N,&Z_MONE,WORK,&IONE,V,&IONE,A,&LDA);
magma_free_cpu(WORK);
}
inline static void
magma_dlarfxsym_v2(magma_int_t n,
double *A, magma_int_t lda,
double *V, double *TAU,
double *work)
{
/*
WORK (workspace) double real array, dimension N
*/
magma_int_t ione = 1;
double dtmp;
double c_zero = MAGMA_D_ZERO;
double c_neg_one= MAGMA_D_NEG_ONE;
double c_half = MAGMA_D_HALF;
/* X = AVtau */
blasf77_dsymv("L",&n, TAU, A, &lda, V, &ione, &c_zero, work, &ione);
/* compute dtmp= X'*V */
#if defined(PRECISION_z) || defined(PRECISION_c)
dtmp = c_zero;
for (magma_int_t j = 0; j < n; j++)
dtmp = dtmp + MAGMA_D_CNJG(work[j]) * V[j];
//cblas_ddot_sub(n, work, ione, V, ione, &dtmp);
#else
dtmp = cblas_ddot(n, work, ione, V, ione);
#endif
/* compute 1/2 X'*V*t = 1/2*dtmp*tau */
dtmp = -dtmp * c_half * (*TAU);
/* compute W=X-1/2VX'Vt = X - dtmp*V */
blasf77_daxpy(&n, &dtmp, V, &ione, work, &ione);
/* performs the symmetric rank 2 operation A := alpha*x*y' + alpha*y*x' + A */
blasf77_dsyr2("L", &n, &c_neg_one, work, &ione, V, &ione, A, &lda);
}