MAGMA  1.7.0
Matrix Algebra for GPU and Multicore Architectures
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double precision

Functions

void magmablas_dlarfg_q (magma_int_t n, magmaDouble_ptr dalpha, magmaDouble_ptr dx, magma_int_t incx, magmaDouble_ptr dtau, magma_queue_t queue)
 DLARFG generates a real elementary reflector (Householder matrix) H of order n, such that. More...
 
void magmablas_dlarfg (magma_int_t n, magmaDouble_ptr dalpha, magmaDouble_ptr dx, magma_int_t incx, magmaDouble_ptr dtau)
 

Detailed Description

Function Documentation

void magmablas_dlarfg ( magma_int_t  n,
magmaDouble_ptr  dalpha,
magmaDouble_ptr  dx,
magma_int_t  incx,
magmaDouble_ptr  dtau 
)
void magmablas_dlarfg_q ( magma_int_t  n,
magmaDouble_ptr  dalpha,
magmaDouble_ptr  dx,
magma_int_t  incx,
magmaDouble_ptr  dtau,
magma_queue_t  queue 
)

DLARFG generates a real elementary reflector (Householder matrix) H of order n, such that.

H * ( alpha ) = ( beta ), H**H * H = I. ( x ) ( 0 )

where alpha and beta are scalars, with beta real and beta = ±norm([alpha, x]), and x is an (n-1)-element real vector. H is represented in the form

 H = I - tau * ( 1 ) * ( 1 v**H ),
               ( v )

where tau is a real scalar and v is a real (n-1)-element vector. Note that H is not symmetric.

If the elements of x are all zero and dalpha is real, then tau = 0 and H is taken to be the unit matrix.

Otherwise 1 <= real(tau) <= 2 and abs(tau-1) <= 1.

Parameters
[in]nINTEGER The order of the elementary reflector.
[in,out]dalphaDOUBLE_PRECISION* on the GPU. On entry, pointer to the value alpha, i.e., the first entry of the vector. On exit, it is overwritten with the value beta.
[in,out]dxDOUBLE_PRECISION array, dimension (1+(N-2)*abs(INCX)), on the GPU On entry, the (n-1)-element vector x. On exit, it is overwritten with the vector v.
[in]incxINTEGER The increment between elements of X. INCX > 0.
[out]dtauDOUBLE_PRECISION* on the GPU. Pointer to the value tau.
[in]queuemagma_queue_t Queue to execute in.