LAPACK  3.10.0
LAPACK: Linear Algebra PACKage
slauu2.f
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1 *> \brief \b SLAUU2 computes the product UUH or LHL, where U and L are upper or lower triangular matrices (unblocked algorithm).
2 *
3 * =========== DOCUMENTATION ===========
4 *
5 * Online html documentation available at
6 * http://www.netlib.org/lapack/explore-html/
7 *
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15 *> [TXT]</a>
16 *> \endhtmlonly
17 *
18 * Definition:
19 * ===========
20 *
21 * SUBROUTINE SLAUU2( UPLO, N, A, LDA, INFO )
22 *
23 * .. Scalar Arguments ..
24 * CHARACTER UPLO
25 * INTEGER INFO, LDA, N
26 * ..
27 * .. Array Arguments ..
28 * REAL A( LDA, * )
29 * ..
30 *
31 *
32 *> \par Purpose:
33 * =============
34 *>
35 *> \verbatim
36 *>
37 *> SLAUU2 computes the product U * U**T or L**T * L, where the triangular
38 *> factor U or L is stored in the upper or lower triangular part of
39 *> the array A.
40 *>
41 *> If UPLO = 'U' or 'u' then the upper triangle of the result is stored,
42 *> overwriting the factor U in A.
43 *> If UPLO = 'L' or 'l' then the lower triangle of the result is stored,
44 *> overwriting the factor L in A.
45 *>
46 *> This is the unblocked form of the algorithm, calling Level 2 BLAS.
47 *> \endverbatim
48 *
49 * Arguments:
50 * ==========
51 *
52 *> \param[in] UPLO
53 *> \verbatim
54 *> UPLO is CHARACTER*1
55 *> Specifies whether the triangular factor stored in the array A
56 *> is upper or lower triangular:
57 *> = 'U': Upper triangular
58 *> = 'L': Lower triangular
59 *> \endverbatim
60 *>
61 *> \param[in] N
62 *> \verbatim
63 *> N is INTEGER
64 *> The order of the triangular factor U or L. N >= 0.
65 *> \endverbatim
66 *>
67 *> \param[in,out] A
68 *> \verbatim
69 *> A is REAL array, dimension (LDA,N)
70 *> On entry, the triangular factor U or L.
71 *> On exit, if UPLO = 'U', the upper triangle of A is
72 *> overwritten with the upper triangle of the product U * U**T;
73 *> if UPLO = 'L', the lower triangle of A is overwritten with
74 *> the lower triangle of the product L**T * L.
75 *> \endverbatim
76 *>
77 *> \param[in] LDA
78 *> \verbatim
79 *> LDA is INTEGER
80 *> The leading dimension of the array A. LDA >= max(1,N).
81 *> \endverbatim
82 *>
83 *> \param[out] INFO
84 *> \verbatim
85 *> INFO is INTEGER
86 *> = 0: successful exit
87 *> < 0: if INFO = -k, the k-th argument had an illegal value
88 *> \endverbatim
89 *
90 * Authors:
91 * ========
92 *
93 *> \author Univ. of Tennessee
94 *> \author Univ. of California Berkeley
95 *> \author Univ. of Colorado Denver
96 *> \author NAG Ltd.
97 *
98 *> \ingroup realOTHERauxiliary
99 *
100 * =====================================================================
101  SUBROUTINE slauu2( UPLO, N, A, LDA, INFO )
102 *
103 * -- LAPACK auxiliary routine --
104 * -- LAPACK is a software package provided by Univ. of Tennessee, --
105 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
106 *
107 * .. Scalar Arguments ..
108  CHARACTER UPLO
109  INTEGER INFO, LDA, N
110 * ..
111 * .. Array Arguments ..
112  REAL A( LDA, * )
113 * ..
114 *
115 * =====================================================================
116 *
117 * .. Parameters ..
118  REAL ONE
119  parameter( one = 1.0e+0 )
120 * ..
121 * .. Local Scalars ..
122  LOGICAL UPPER
123  INTEGER I
124  REAL AII
125 * ..
126 * .. External Functions ..
127  LOGICAL LSAME
128  REAL SDOT
129  EXTERNAL lsame, sdot
130 * ..
131 * .. External Subroutines ..
132  EXTERNAL sgemv, sscal, xerbla
133 * ..
134 * .. Intrinsic Functions ..
135  INTRINSIC max
136 * ..
137 * .. Executable Statements ..
138 *
139 * Test the input parameters.
140 *
141  info = 0
142  upper = lsame( uplo, 'U' )
143  IF( .NOT.upper .AND. .NOT.lsame( uplo, 'L' ) ) THEN
144  info = -1
145  ELSE IF( n.LT.0 ) THEN
146  info = -2
147  ELSE IF( lda.LT.max( 1, n ) ) THEN
148  info = -4
149  END IF
150  IF( info.NE.0 ) THEN
151  CALL xerbla( 'SLAUU2', -info )
152  RETURN
153  END IF
154 *
155 * Quick return if possible
156 *
157  IF( n.EQ.0 )
158  $ RETURN
159 *
160  IF( upper ) THEN
161 *
162 * Compute the product U * U**T.
163 *
164  DO 10 i = 1, n
165  aii = a( i, i )
166  IF( i.LT.n ) THEN
167  a( i, i ) = sdot( n-i+1, a( i, i ), lda, a( i, i ), lda )
168  CALL sgemv( 'No transpose', i-1, n-i, one, a( 1, i+1 ),
169  $ lda, a( i, i+1 ), lda, aii, a( 1, i ), 1 )
170  ELSE
171  CALL sscal( i, aii, a( 1, i ), 1 )
172  END IF
173  10 CONTINUE
174 *
175  ELSE
176 *
177 * Compute the product L**T * L.
178 *
179  DO 20 i = 1, n
180  aii = a( i, i )
181  IF( i.LT.n ) THEN
182  a( i, i ) = sdot( n-i+1, a( i, i ), 1, a( i, i ), 1 )
183  CALL sgemv( 'Transpose', n-i, i-1, one, a( i+1, 1 ), lda,
184  $ a( i+1, i ), 1, aii, a( i, 1 ), lda )
185  ELSE
186  CALL sscal( i, aii, a( i, 1 ), lda )
187  END IF
188  20 CONTINUE
189  END IF
190 *
191  RETURN
192 *
193 * End of SLAUU2
194 *
195  END
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
subroutine slauu2(UPLO, N, A, LDA, INFO)
SLAUU2 computes the product UUH or LHL, where U and L are upper or lower triangular matrices (unblock...
Definition: slauu2.f:102
subroutine sscal(N, SA, SX, INCX)
SSCAL
Definition: sscal.f:79
subroutine sgemv(TRANS, M, N, ALPHA, A, LDA, X, INCX, BETA, Y, INCY)
SGEMV
Definition: sgemv.f:156