1*> \brief \b CSYR performs the symmetric rank-1 update of a complex symmetric matrix.
2*
3*  =========== DOCUMENTATION ===========
4*
5* Online html documentation available at
6*            http://www.netlib.org/lapack/explore-html/
7*
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16*> \endhtmlonly
17*
18*  Definition:
19*  ===========
20*
21*       SUBROUTINE CSYR( UPLO, N, ALPHA, X, INCX, A, LDA )
22*
23*       .. Scalar Arguments ..
24*       CHARACTER          UPLO
25*       INTEGER            INCX, LDA, N
26*       COMPLEX            ALPHA
27*       ..
28*       .. Array Arguments ..
29*       COMPLEX            A( LDA, * ), X( * )
30*       ..
31*
32*
33*> \par Purpose:
34*  =============
35*>
36*> \verbatim
37*>
38*> CSYR   performs the symmetric rank 1 operation
39*>
40*>    A := alpha*x*x**H + A,
41*>
42*> where alpha is a complex scalar, x is an n element vector and A is an
43*> n by n symmetric matrix.
44*> \endverbatim
45*
46*  Arguments:
47*  ==========
48*
49*> \param[in] UPLO
50*> \verbatim
51*>          UPLO is CHARACTER*1
52*>           On entry, UPLO specifies whether the upper or lower
53*>           triangular part of the array A is to be referenced as
54*>           follows:
55*>
56*>              UPLO = 'U' or 'u'   Only the upper triangular part of A
57*>                                  is to be referenced.
58*>
59*>              UPLO = 'L' or 'l'   Only the lower triangular part of A
60*>                                  is to be referenced.
61*>
62*>           Unchanged on exit.
63*> \endverbatim
64*>
65*> \param[in] N
66*> \verbatim
67*>          N is INTEGER
68*>           On entry, N specifies the order of the matrix A.
69*>           N must be at least zero.
70*>           Unchanged on exit.
71*> \endverbatim
72*>
73*> \param[in] ALPHA
74*> \verbatim
75*>          ALPHA is COMPLEX
76*>           On entry, ALPHA specifies the scalar alpha.
77*>           Unchanged on exit.
78*> \endverbatim
79*>
80*> \param[in] X
81*> \verbatim
82*>          X is COMPLEX array, dimension at least
83*>           ( 1 + ( N - 1 )*abs( INCX ) ).
84*>           Before entry, the incremented array X must contain the N-
85*>           element vector x.
86*>           Unchanged on exit.
87*> \endverbatim
88*>
89*> \param[in] INCX
90*> \verbatim
91*>          INCX is INTEGER
92*>           On entry, INCX specifies the increment for the elements of
93*>           X. INCX must not be zero.
94*>           Unchanged on exit.
95*> \endverbatim
96*>
97*> \param[in,out] A
98*> \verbatim
99*>          A is COMPLEX array, dimension ( LDA, N )
100*>           Before entry, with  UPLO = 'U' or 'u', the leading n by n
101*>           upper triangular part of the array A must contain the upper
102*>           triangular part of the symmetric matrix and the strictly
103*>           lower triangular part of A is not referenced. On exit, the
104*>           upper triangular part of the array A is overwritten by the
105*>           upper triangular part of the updated matrix.
106*>           Before entry, with UPLO = 'L' or 'l', the leading n by n
107*>           lower triangular part of the array A must contain the lower
108*>           triangular part of the symmetric matrix and the strictly
109*>           upper triangular part of A is not referenced. On exit, the
110*>           lower triangular part of the array A is overwritten by the
111*>           lower triangular part of the updated matrix.
112*> \endverbatim
113*>
114*> \param[in] LDA
115*> \verbatim
116*>          LDA is INTEGER
117*>           On entry, LDA specifies the first dimension of A as declared
118*>           in the calling (sub) program. LDA must be at least
119*>           max( 1, N ).
120*>           Unchanged on exit.
121*> \endverbatim
122*
123*  Authors:
124*  ========
125*
126*> \author Univ. of Tennessee
127*> \author Univ. of California Berkeley
128*> \author Univ. of Colorado Denver
129*> \author NAG Ltd.
130*
131*> \ingroup complexSYauxiliary
132*
133*  =====================================================================
134      SUBROUTINE CSYR( UPLO, N, ALPHA, X, INCX, A, LDA )
135*
136*  -- LAPACK auxiliary routine --
137*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
138*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
139*
140*     .. Scalar Arguments ..
141      CHARACTER          UPLO
142      INTEGER            INCX, LDA, N
143      COMPLEX            ALPHA
144*     ..
145*     .. Array Arguments ..
146      COMPLEX            A( LDA, * ), X( * )
147*     ..
148*
149* =====================================================================
150*
151*     .. Parameters ..
152      COMPLEX            ZERO
153      PARAMETER          ( ZERO = ( 0.0E+0, 0.0E+0 ) )
154*     ..
155*     .. Local Scalars ..
156      INTEGER            I, INFO, IX, J, JX, KX
157      COMPLEX            TEMP
158*     ..
159*     .. External Functions ..
160      LOGICAL            LSAME
161      EXTERNAL           LSAME
162*     ..
163*     .. External Subroutines ..
164      EXTERNAL           XERBLA
165*     ..
166*     .. Intrinsic Functions ..
167      INTRINSIC          MAX
168*     ..
169*     .. Executable Statements ..
170*
171*     Test the input parameters.
172*
173      INFO = 0
174      IF( .NOT.LSAME( UPLO, 'U' ) .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
175         INFO = 1
176      ELSE IF( N.LT.0 ) THEN
177         INFO = 2
178      ELSE IF( INCX.EQ.0 ) THEN
179         INFO = 5
180      ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
181         INFO = 7
182      END IF
183      IF( INFO.NE.0 ) THEN
184         CALL XERBLA( 'CSYR  ', INFO )
185         RETURN
186      END IF
187*
188*     Quick return if possible.
189*
190      IF( ( N.EQ.0 ) .OR. ( ALPHA.EQ.ZERO ) )
191     $   RETURN
192*
193*     Set the start point in X if the increment is not unity.
194*
195      IF( INCX.LE.0 ) THEN
196         KX = 1 - ( N-1 )*INCX
197      ELSE IF( INCX.NE.1 ) THEN
198         KX = 1
199      END IF
200*
201*     Start the operations. In this version the elements of A are
202*     accessed sequentially with one pass through the triangular part
203*     of A.
204*
205      IF( LSAME( UPLO, 'U' ) ) THEN
206*
207*        Form  A  when A is stored in upper triangle.
208*
209         IF( INCX.EQ.1 ) THEN
210            DO 20 J = 1, N
211               IF( X( J ).NE.ZERO ) THEN
212                  TEMP = ALPHA*X( J )
213                  DO 10 I = 1, J
214                     A( I, J ) = A( I, J ) + X( I )*TEMP
215   10             CONTINUE
216               END IF
217   20       CONTINUE
218         ELSE
219            JX = KX
220            DO 40 J = 1, N
221               IF( X( JX ).NE.ZERO ) THEN
222                  TEMP = ALPHA*X( JX )
223                  IX = KX
224                  DO 30 I = 1, J
225                     A( I, J ) = A( I, J ) + X( IX )*TEMP
226                     IX = IX + INCX
227   30             CONTINUE
228               END IF
229               JX = JX + INCX
230   40       CONTINUE
231         END IF
232      ELSE
233*
234*        Form  A  when A is stored in lower triangle.
235*
236         IF( INCX.EQ.1 ) THEN
237            DO 60 J = 1, N
238               IF( X( J ).NE.ZERO ) THEN
239                  TEMP = ALPHA*X( J )
240                  DO 50 I = J, N
241                     A( I, J ) = A( I, J ) + X( I )*TEMP
242   50             CONTINUE
243               END IF
244   60       CONTINUE
245         ELSE
246            JX = KX
247            DO 80 J = 1, N
248               IF( X( JX ).NE.ZERO ) THEN
249                  TEMP = ALPHA*X( JX )
250                  IX = JX
251                  DO 70 I = J, N
252                     A( I, J ) = A( I, J ) + X( IX )*TEMP
253                     IX = IX + INCX
254   70             CONTINUE
255               END IF
256               JX = JX + INCX
257   80       CONTINUE
258         END IF
259      END IF
260*
261      RETURN
262*
263*     End of CSYR
264*
265      END
266