Visible to Intel only — GUID: GUID-BC9F3571-D003-48A8-A893-1A93BB51A2EE
Visible to Intel only — GUID: GUID-BC9F3571-D003-48A8-A893-1A93BB51A2EE
?larfg
Generates an elementary reflector (Householder matrix).
Syntax
lapack_int LAPACKE_slarfg (lapack_int n , float * alpha , float * x , lapack_int incx , float * tau );
lapack_int LAPACKE_dlarfg (lapack_int n , double * alpha , double * x , lapack_int incx , double * tau );
lapack_int LAPACKE_clarfg (lapack_int n , lapack_complex_float * alpha , lapack_complex_float * x , lapack_int incx , lapack_complex_float * tau );
lapack_int LAPACKE_zlarfg (lapack_int n , lapack_complex_double * alpha , lapack_complex_double * x , lapack_int incx , lapack_complex_double * tau );
Include Files
- mkl.h
Description
The routine ?larfg generates a real/complex elementary reflector H of order n, such that
for real flavors and
for complex flavors,
where alpha and beta are scalars (with beta real for all flavors), and x is an (n-1)-element real/complex vector. H is represented in the form
for real flavors and
for complex flavors,
where tau is a real/complex scalar and v is a real/complex (n-1)-element vector, respectively. Note that for clarfg/zlarfg, H is not Hermitian.
If the elements of x are all zero (and, for complex flavors, alpha is real), then tau = 0 and H is taken to be the unit matrix.
Otherwise, 1 ≤ tau ≤ 2 (for real flavors), or
1 ≤ Re(tau) ≤ 2 and abs(tau-1) ≤ 1 (for complex flavors).
Input Parameters
A <datatype> placeholder, if present, is used for the C interface data types in the C interface section above. See C Interface Conventions for the C interface principal conventions and type definitions.
- n
-
The order of the elementary reflector.
- alpha
- x
-
Array, size (1+(n-2)*abs(incx)).
On entry, the vector x.
- incx
-
The increment between elements of x. incx > 0.
Output Parameters
- alpha
-
On exit, it is overwritten with the value beta.
- x
-
On exit, it is overwritten with the vector v.
- tau
Return Values
This function returns a value info.
If info = 0, the execution is successful.
If info = -2, alpha is NaN
If info = -3, array x contains NaN components.