 LAPACK  3.6.1 LAPACK: Linear Algebra PACKage
 subroutine slarfy ( character UPLO, integer N, real, dimension( * ) V, integer INCV, real TAU, real, dimension( ldc, * ) C, integer LDC, real, dimension( * ) WORK )

SLARFY

Purpose:
``` SLARFY applies an elementary reflector, or Householder matrix, H,
to an n x n symmetric matrix C, from both the left and the right.

H is represented in the form

H = I - tau * v * v'

where  tau  is a scalar and  v  is a vector.

If  tau  is  zero, then  H  is taken to be the unit matrix.```
Parameters
 [in] UPLO ``` UPLO is CHARACTER*1 Specifies whether the upper or lower triangular part of the symmetric matrix C is stored. = 'U': Upper triangle = 'L': Lower triangle``` [in] N ``` N is INTEGER The number of rows and columns of the matrix C. N >= 0.``` [in] V ``` V is REAL array, dimension (1 + (N-1)*abs(INCV)) The vector v as described above.``` [in] INCV ``` INCV is INTEGER The increment between successive elements of v. INCV must not be zero.``` [in] TAU ``` TAU is REAL The value tau as described above.``` [in,out] C ``` C is REAL array, dimension (LDC, N) On entry, the matrix C. On exit, C is overwritten by H * C * H'.``` [in] LDC ``` LDC is INTEGER The leading dimension of the array C. LDC >= max( 1, N ).``` [out] WORK ` WORK is REAL array, dimension (N)`
Date
November 2011

Definition at line 110 of file slarfy.f.

110 *
111 * -- LAPACK test routine (version 3.4.0) --
112 * -- LAPACK is a software package provided by Univ. of Tennessee, --
113 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
114 * November 2011
115 *
116 * .. Scalar Arguments ..
117  CHARACTER uplo
118  INTEGER incv, ldc, n
119  REAL tau
120 * ..
121 * .. Array Arguments ..
122  REAL c( ldc, * ), v( * ), work( * )
123 * ..
124 *
125 * =====================================================================
126 *
127 * .. Parameters ..
128  REAL one, zero, half
129  parameter ( one = 1.0e+0, zero = 0.0e+0, half = 0.5e+0 )
130 * ..
131 * .. Local Scalars ..
132  REAL alpha
133 * ..
134 * .. External Subroutines ..
135  EXTERNAL saxpy, ssymv, ssyr2
136 * ..
137 * .. External Functions ..
138  REAL sdot
139  EXTERNAL sdot
140 * ..
141 * .. Executable Statements ..
142 *
143  IF( tau.EQ.zero )
144  \$ RETURN
145 *
146 * Form w:= C * v
147 *
148  CALL ssymv( uplo, n, one, c, ldc, v, incv, zero, work, 1 )
149 *
150  alpha = -half*tau*sdot( n, work, 1, v, incv )
151  CALL saxpy( n, alpha, v, incv, work, 1 )
152 *
153 * C := C - v * w' - w * v'
154 *
155  CALL ssyr2( uplo, n, -tau, v, incv, work, 1, c, ldc )
156 *
157  RETURN
158 *
159 * End of SLARFY
160 *
subroutine ssyr2(UPLO, N, ALPHA, X, INCX, Y, INCY, A, LDA)
SSYR2
Definition: ssyr2.f:149
real function sdot(N, SX, INCX, SY, INCY)
SDOT
Definition: sdot.f:53
subroutine saxpy(N, SA, SX, INCX, SY, INCY)
SAXPY
Definition: saxpy.f:54
subroutine ssymv(UPLO, N, ALPHA, A, LDA, X, INCX, BETA, Y, INCY)
SSYMV
Definition: ssymv.f:154

Here is the call graph for this function:

Here is the caller graph for this function: