LAPACK  3.10.0
LAPACK: Linear Algebra PACKage
ssyr.f
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1 *> \brief \b SSYR
2 *
3 * =========== DOCUMENTATION ===========
4 *
5 * Online html documentation available at
6 * http://www.netlib.org/lapack/explore-html/
7 *
8 * Definition:
9 * ===========
10 *
11 * SUBROUTINE SSYR(UPLO,N,ALPHA,X,INCX,A,LDA)
12 *
13 * .. Scalar Arguments ..
14 * REAL ALPHA
15 * INTEGER INCX,LDA,N
16 * CHARACTER UPLO
17 * ..
18 * .. Array Arguments ..
19 * REAL A(LDA,*),X(*)
20 * ..
21 *
22 *
23 *> \par Purpose:
24 * =============
25 *>
26 *> \verbatim
27 *>
28 *> SSYR performs the symmetric rank 1 operation
29 *>
30 *> A := alpha*x*x**T + A,
31 *>
32 *> where alpha is a real scalar, x is an n element vector and A is an
33 *> n by n symmetric matrix.
34 *> \endverbatim
35 *
36 * Arguments:
37 * ==========
38 *
39 *> \param[in] UPLO
40 *> \verbatim
41 *> UPLO is CHARACTER*1
42 *> On entry, UPLO specifies whether the upper or lower
43 *> triangular part of the array A is to be referenced as
44 *> follows:
45 *>
46 *> UPLO = 'U' or 'u' Only the upper triangular part of A
47 *> is to be referenced.
48 *>
49 *> UPLO = 'L' or 'l' Only the lower triangular part of A
50 *> is to be referenced.
51 *> \endverbatim
52 *>
53 *> \param[in] N
54 *> \verbatim
55 *> N is INTEGER
56 *> On entry, N specifies the order of the matrix A.
57 *> N must be at least zero.
58 *> \endverbatim
59 *>
60 *> \param[in] ALPHA
61 *> \verbatim
62 *> ALPHA is REAL
63 *> On entry, ALPHA specifies the scalar alpha.
64 *> \endverbatim
65 *>
66 *> \param[in] X
67 *> \verbatim
68 *> X is REAL array, dimension at least
69 *> ( 1 + ( n - 1 )*abs( INCX ) ).
70 *> Before entry, the incremented array X must contain the n
71 *> element vector x.
72 *> \endverbatim
73 *>
74 *> \param[in] INCX
75 *> \verbatim
76 *> INCX is INTEGER
77 *> On entry, INCX specifies the increment for the elements of
78 *> X. INCX must not be zero.
79 *> \endverbatim
80 *>
81 *> \param[in,out] A
82 *> \verbatim
83 *> A is REAL array, dimension ( LDA, N )
84 *> Before entry with UPLO = 'U' or 'u', the leading n by n
85 *> upper triangular part of the array A must contain the upper
86 *> triangular part of the symmetric matrix and the strictly
87 *> lower triangular part of A is not referenced. On exit, the
88 *> upper triangular part of the array A is overwritten by the
89 *> upper triangular part of the updated matrix.
90 *> Before entry with UPLO = 'L' or 'l', the leading n by n
91 *> lower triangular part of the array A must contain the lower
92 *> triangular part of the symmetric matrix and the strictly
93 *> upper triangular part of A is not referenced. On exit, the
94 *> lower triangular part of the array A is overwritten by the
95 *> lower triangular part of the updated matrix.
96 *> \endverbatim
97 *>
98 *> \param[in] LDA
99 *> \verbatim
100 *> LDA is INTEGER
101 *> On entry, LDA specifies the first dimension of A as declared
102 *> in the calling (sub) program. LDA must be at least
103 *> max( 1, n ).
104 *> \endverbatim
105 *
106 * Authors:
107 * ========
108 *
109 *> \author Univ. of Tennessee
110 *> \author Univ. of California Berkeley
111 *> \author Univ. of Colorado Denver
112 *> \author NAG Ltd.
113 *
114 *> \ingroup single_blas_level2
115 *
116 *> \par Further Details:
117 * =====================
118 *>
119 *> \verbatim
120 *>
121 *> Level 2 Blas routine.
122 *>
123 *> -- Written on 22-October-1986.
124 *> Jack Dongarra, Argonne National Lab.
125 *> Jeremy Du Croz, Nag Central Office.
126 *> Sven Hammarling, Nag Central Office.
127 *> Richard Hanson, Sandia National Labs.
128 *> \endverbatim
129 *>
130 * =====================================================================
131  SUBROUTINE ssyr(UPLO,N,ALPHA,X,INCX,A,LDA)
132 *
133 * -- Reference BLAS level2 routine --
134 * -- Reference BLAS is a software package provided by Univ. of Tennessee, --
135 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
136 *
137 * .. Scalar Arguments ..
138  REAL ALPHA
139  INTEGER INCX,LDA,N
140  CHARACTER UPLO
141 * ..
142 * .. Array Arguments ..
143  REAL A(LDA,*),X(*)
144 * ..
145 *
146 * =====================================================================
147 *
148 * .. Parameters ..
149  REAL ZERO
150  parameter(zero=0.0e+0)
151 * ..
152 * .. Local Scalars ..
153  REAL TEMP
154  INTEGER I,INFO,IX,J,JX,KX
155 * ..
156 * .. External Functions ..
157  LOGICAL LSAME
158  EXTERNAL lsame
159 * ..
160 * .. External Subroutines ..
161  EXTERNAL xerbla
162 * ..
163 * .. Intrinsic Functions ..
164  INTRINSIC max
165 * ..
166 *
167 * Test the input parameters.
168 *
169  info = 0
170  IF (.NOT.lsame(uplo,'U') .AND. .NOT.lsame(uplo,'L')) THEN
171  info = 1
172  ELSE IF (n.LT.0) THEN
173  info = 2
174  ELSE IF (incx.EQ.0) THEN
175  info = 5
176  ELSE IF (lda.LT.max(1,n)) THEN
177  info = 7
178  END IF
179  IF (info.NE.0) THEN
180  CALL xerbla('SSYR ',info)
181  RETURN
182  END IF
183 *
184 * Quick return if possible.
185 *
186  IF ((n.EQ.0) .OR. (alpha.EQ.zero)) RETURN
187 *
188 * Set the start point in X if the increment is not unity.
189 *
190  IF (incx.LE.0) THEN
191  kx = 1 - (n-1)*incx
192  ELSE IF (incx.NE.1) THEN
193  kx = 1
194  END IF
195 *
196 * Start the operations. In this version the elements of A are
197 * accessed sequentially with one pass through the triangular part
198 * of A.
199 *
200  IF (lsame(uplo,'U')) THEN
201 *
202 * Form A when A is stored in upper triangle.
203 *
204  IF (incx.EQ.1) THEN
205  DO 20 j = 1,n
206  IF (x(j).NE.zero) THEN
207  temp = alpha*x(j)
208  DO 10 i = 1,j
209  a(i,j) = a(i,j) + x(i)*temp
210  10 CONTINUE
211  END IF
212  20 CONTINUE
213  ELSE
214  jx = kx
215  DO 40 j = 1,n
216  IF (x(jx).NE.zero) THEN
217  temp = alpha*x(jx)
218  ix = kx
219  DO 30 i = 1,j
220  a(i,j) = a(i,j) + x(ix)*temp
221  ix = ix + incx
222  30 CONTINUE
223  END IF
224  jx = jx + incx
225  40 CONTINUE
226  END IF
227  ELSE
228 *
229 * Form A when A is stored in lower triangle.
230 *
231  IF (incx.EQ.1) THEN
232  DO 60 j = 1,n
233  IF (x(j).NE.zero) THEN
234  temp = alpha*x(j)
235  DO 50 i = j,n
236  a(i,j) = a(i,j) + x(i)*temp
237  50 CONTINUE
238  END IF
239  60 CONTINUE
240  ELSE
241  jx = kx
242  DO 80 j = 1,n
243  IF (x(jx).NE.zero) THEN
244  temp = alpha*x(jx)
245  ix = jx
246  DO 70 i = j,n
247  a(i,j) = a(i,j) + x(ix)*temp
248  ix = ix + incx
249  70 CONTINUE
250  END IF
251  jx = jx + incx
252  80 CONTINUE
253  END IF
254  END IF
255 *
256  RETURN
257 *
258 * End of SSYR
259 *
260  END
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
subroutine ssyr(UPLO, N, ALPHA, X, INCX, A, LDA)
SSYR
Definition: ssyr.f:132