LAPACK  3.10.0 LAPACK: Linear Algebra PACKage
cspmv.f
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1 *> \brief \b CSPMV computes a matrix-vector product for complex vectors using a complex symmetric packed matrix
2 *
3 * =========== DOCUMENTATION ===========
4 *
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17 *
18 * Definition:
19 * ===========
20 *
21 * SUBROUTINE CSPMV( UPLO, N, ALPHA, AP, X, INCX, BETA, Y, INCY )
22 *
23 * .. Scalar Arguments ..
24 * CHARACTER UPLO
25 * INTEGER INCX, INCY, N
26 * COMPLEX ALPHA, BETA
27 * ..
28 * .. Array Arguments ..
29 * COMPLEX AP( * ), X( * ), Y( * )
30 * ..
31 *
32 *
33 *> \par Purpose:
34 * =============
35 *>
36 *> \verbatim
37 *>
38 *> CSPMV performs the matrix-vector operation
39 *>
40 *> y := alpha*A*x + beta*y,
41 *>
42 *> where alpha and beta are scalars, x and y are n element vectors and
43 *> A is an n by n symmetric matrix, supplied in packed form.
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 matrix A is supplied in the packed
54 *> array AP as follows:
55 *>
56 *> UPLO = 'U' or 'u' The upper triangular part of A is
57 *> supplied in AP.
58 *>
59 *> UPLO = 'L' or 'l' The lower triangular part of A is
60 *> supplied in AP.
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] AP
81 *> \verbatim
82 *> AP is COMPLEX array, dimension at least
83 *> ( ( N*( N + 1 ) )/2 ).
84 *> Before entry, with UPLO = 'U' or 'u', the array AP must
85 *> contain the upper triangular part of the symmetric matrix
86 *> packed sequentially, column by column, so that AP( 1 )
87 *> contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 1, 2 )
88 *> and a( 2, 2 ) respectively, and so on.
89 *> Before entry, with UPLO = 'L' or 'l', the array AP must
90 *> contain the lower triangular part of the symmetric matrix
91 *> packed sequentially, column by column, so that AP( 1 )
92 *> contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 2, 1 )
93 *> and a( 3, 1 ) respectively, and so on.
94 *> Unchanged on exit.
95 *> \endverbatim
96 *>
97 *> \param[in] X
98 *> \verbatim
99 *> X is COMPLEX array, dimension at least
100 *> ( 1 + ( N - 1 )*abs( INCX ) ).
101 *> Before entry, the incremented array X must contain the N-
102 *> element vector x.
103 *> Unchanged on exit.
104 *> \endverbatim
105 *>
106 *> \param[in] INCX
107 *> \verbatim
108 *> INCX is INTEGER
109 *> On entry, INCX specifies the increment for the elements of
110 *> X. INCX must not be zero.
111 *> Unchanged on exit.
112 *> \endverbatim
113 *>
114 *> \param[in] BETA
115 *> \verbatim
116 *> BETA is COMPLEX
117 *> On entry, BETA specifies the scalar beta. When BETA is
118 *> supplied as zero then Y need not be set on input.
119 *> Unchanged on exit.
120 *> \endverbatim
121 *>
122 *> \param[in,out] Y
123 *> \verbatim
124 *> Y is COMPLEX array, dimension at least
125 *> ( 1 + ( N - 1 )*abs( INCY ) ).
126 *> Before entry, the incremented array Y must contain the n
127 *> element vector y. On exit, Y is overwritten by the updated
128 *> vector y.
129 *> \endverbatim
130 *>
131 *> \param[in] INCY
132 *> \verbatim
133 *> INCY is INTEGER
134 *> On entry, INCY specifies the increment for the elements of
135 *> Y. INCY must not be zero.
136 *> Unchanged on exit.
137 *> \endverbatim
138 *
139 * Authors:
140 * ========
141 *
142 *> \author Univ. of Tennessee
143 *> \author Univ. of California Berkeley
144 *> \author Univ. of Colorado Denver
145 *> \author NAG Ltd.
146 *
147 *> \ingroup complexOTHERauxiliary
148 *
149 * =====================================================================
150  SUBROUTINE cspmv( UPLO, N, ALPHA, AP, X, INCX, BETA, Y, INCY )
151 *
152 * -- LAPACK auxiliary routine --
153 * -- LAPACK is a software package provided by Univ. of Tennessee, --
154 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
155 *
156 * .. Scalar Arguments ..
157  CHARACTER UPLO
158  INTEGER INCX, INCY, N
159  COMPLEX ALPHA, BETA
160 * ..
161 * .. Array Arguments ..
162  COMPLEX AP( * ), X( * ), Y( * )
163 * ..
164 *
165 * =====================================================================
166 *
167 * .. Parameters ..
168  COMPLEX ONE
169  parameter( one = ( 1.0e+0, 0.0e+0 ) )
170  COMPLEX ZERO
171  parameter( zero = ( 0.0e+0, 0.0e+0 ) )
172 * ..
173 * .. Local Scalars ..
174  INTEGER I, INFO, IX, IY, J, JX, JY, K, KK, KX, KY
175  COMPLEX TEMP1, TEMP2
176 * ..
177 * .. External Functions ..
178  LOGICAL LSAME
179  EXTERNAL lsame
180 * ..
181 * .. External Subroutines ..
182  EXTERNAL xerbla
183 * ..
184 * .. Executable Statements ..
185 *
186 * Test the input parameters.
187 *
188  info = 0
189  IF( .NOT.lsame( uplo, 'U' ) .AND. .NOT.lsame( uplo, 'L' ) ) THEN
190  info = 1
191  ELSE IF( n.LT.0 ) THEN
192  info = 2
193  ELSE IF( incx.EQ.0 ) THEN
194  info = 6
195  ELSE IF( incy.EQ.0 ) THEN
196  info = 9
197  END IF
198  IF( info.NE.0 ) THEN
199  CALL xerbla( 'CSPMV ', info )
200  RETURN
201  END IF
202 *
203 * Quick return if possible.
204 *
205  IF( ( n.EQ.0 ) .OR. ( ( alpha.EQ.zero ) .AND. ( beta.EQ.one ) ) )
206  \$ RETURN
207 *
208 * Set up the start points in X and Y.
209 *
210  IF( incx.GT.0 ) THEN
211  kx = 1
212  ELSE
213  kx = 1 - ( n-1 )*incx
214  END IF
215  IF( incy.GT.0 ) THEN
216  ky = 1
217  ELSE
218  ky = 1 - ( n-1 )*incy
219  END IF
220 *
221 * Start the operations. In this version the elements of the array AP
222 * are accessed sequentially with one pass through AP.
223 *
224 * First form y := beta*y.
225 *
226  IF( beta.NE.one ) THEN
227  IF( incy.EQ.1 ) THEN
228  IF( beta.EQ.zero ) THEN
229  DO 10 i = 1, n
230  y( i ) = zero
231  10 CONTINUE
232  ELSE
233  DO 20 i = 1, n
234  y( i ) = beta*y( i )
235  20 CONTINUE
236  END IF
237  ELSE
238  iy = ky
239  IF( beta.EQ.zero ) THEN
240  DO 30 i = 1, n
241  y( iy ) = zero
242  iy = iy + incy
243  30 CONTINUE
244  ELSE
245  DO 40 i = 1, n
246  y( iy ) = beta*y( iy )
247  iy = iy + incy
248  40 CONTINUE
249  END IF
250  END IF
251  END IF
252  IF( alpha.EQ.zero )
253  \$ RETURN
254  kk = 1
255  IF( lsame( uplo, 'U' ) ) THEN
256 *
257 * Form y when AP contains the upper triangle.
258 *
259  IF( ( incx.EQ.1 ) .AND. ( incy.EQ.1 ) ) THEN
260  DO 60 j = 1, n
261  temp1 = alpha*x( j )
262  temp2 = zero
263  k = kk
264  DO 50 i = 1, j - 1
265  y( i ) = y( i ) + temp1*ap( k )
266  temp2 = temp2 + ap( k )*x( i )
267  k = k + 1
268  50 CONTINUE
269  y( j ) = y( j ) + temp1*ap( kk+j-1 ) + alpha*temp2
270  kk = kk + j
271  60 CONTINUE
272  ELSE
273  jx = kx
274  jy = ky
275  DO 80 j = 1, n
276  temp1 = alpha*x( jx )
277  temp2 = zero
278  ix = kx
279  iy = ky
280  DO 70 k = kk, kk + j - 2
281  y( iy ) = y( iy ) + temp1*ap( k )
282  temp2 = temp2 + ap( k )*x( ix )
283  ix = ix + incx
284  iy = iy + incy
285  70 CONTINUE
286  y( jy ) = y( jy ) + temp1*ap( kk+j-1 ) + alpha*temp2
287  jx = jx + incx
288  jy = jy + incy
289  kk = kk + j
290  80 CONTINUE
291  END IF
292  ELSE
293 *
294 * Form y when AP contains the lower triangle.
295 *
296  IF( ( incx.EQ.1 ) .AND. ( incy.EQ.1 ) ) THEN
297  DO 100 j = 1, n
298  temp1 = alpha*x( j )
299  temp2 = zero
300  y( j ) = y( j ) + temp1*ap( kk )
301  k = kk + 1
302  DO 90 i = j + 1, n
303  y( i ) = y( i ) + temp1*ap( k )
304  temp2 = temp2 + ap( k )*x( i )
305  k = k + 1
306  90 CONTINUE
307  y( j ) = y( j ) + alpha*temp2
308  kk = kk + ( n-j+1 )
309  100 CONTINUE
310  ELSE
311  jx = kx
312  jy = ky
313  DO 120 j = 1, n
314  temp1 = alpha*x( jx )
315  temp2 = zero
316  y( jy ) = y( jy ) + temp1*ap( kk )
317  ix = jx
318  iy = jy
319  DO 110 k = kk + 1, kk + n - j
320  ix = ix + incx
321  iy = iy + incy
322  y( iy ) = y( iy ) + temp1*ap( k )
323  temp2 = temp2 + ap( k )*x( ix )
324  110 CONTINUE
325  y( jy ) = y( jy ) + alpha*temp2
326  jx = jx + incx
327  jy = jy + incy
328  kk = kk + ( n-j+1 )
329  120 CONTINUE
330  END IF
331  END IF
332 *
333  RETURN
334 *
335 * End of CSPMV
336 *
337  END
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
subroutine cspmv(UPLO, N, ALPHA, AP, X, INCX, BETA, Y, INCY)
CSPMV computes a matrix-vector product for complex vectors using a complex symmetric packed matrix
Definition: cspmv.f:151