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csbmv.f
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1 *> \brief \b CSBMV
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 CSBMV( UPLO, N, K, ALPHA, A, LDA, X, INCX, BETA, Y,
12 * INCY )
13 *
14 * .. Scalar Arguments ..
15 * CHARACTER UPLO
16 * INTEGER INCX, INCY, K, LDA, N
17 * COMPLEX ALPHA, BETA
18 * ..
19 * .. Array Arguments ..
20 * COMPLEX A( LDA, * ), X( * ), Y( * )
21 * ..
22 *
23 *
24 *> \par Purpose:
25 * =============
26 *>
27 *> \verbatim
28 *>
29 *> CSBMV performs the matrix-vector operation
30 *>
31 *> y := alpha*A*x + beta*y,
32 *>
33 *> where alpha and beta are scalars, x and y are n element vectors and
34 *> A is an n by n symmetric band matrix, with k super-diagonals.
35 *> \endverbatim
36 *
37 * Arguments:
38 * ==========
39 *
40 *> \verbatim
41 *> UPLO - CHARACTER*1
42 *> On entry, UPLO specifies whether the upper or lower
43 *> triangular part of the band matrix A is being supplied as
44 *> follows:
45 *>
46 *> UPLO = 'U' or 'u' The upper triangular part of A is
47 *> being supplied.
48 *>
49 *> UPLO = 'L' or 'l' The lower triangular part of A is
50 *> being supplied.
51 *>
52 *> Unchanged on exit.
53 *>
54 *> N - INTEGER
55 *> On entry, N specifies the order of the matrix A.
56 *> N must be at least zero.
57 *> Unchanged on exit.
58 *>
59 *> K - INTEGER
60 *> On entry, K specifies the number of super-diagonals of the
61 *> matrix A. K must satisfy 0 .le. K.
62 *> Unchanged on exit.
63 *>
64 *> ALPHA - COMPLEX
65 *> On entry, ALPHA specifies the scalar alpha.
66 *> Unchanged on exit.
67 *>
68 *> A - COMPLEX array, dimension( LDA, N )
69 *> Before entry with UPLO = 'U' or 'u', the leading ( k + 1 )
70 *> by n part of the array A must contain the upper triangular
71 *> band part of the symmetric matrix, supplied column by
72 *> column, with the leading diagonal of the matrix in row
73 *> ( k + 1 ) of the array, the first super-diagonal starting at
74 *> position 2 in row k, and so on. The top left k by k triangle
75 *> of the array A is not referenced.
76 *> The following program segment will transfer the upper
77 *> triangular part of a symmetric band matrix from conventional
78 *> full matrix storage to band storage:
79 *>
80 *> DO 20, J = 1, N
81 *> M = K + 1 - J
82 *> DO 10, I = MAX( 1, J - K ), J
83 *> A( M + I, J ) = matrix( I, J )
84 *> 10 CONTINUE
85 *> 20 CONTINUE
86 *>
87 *> Before entry with UPLO = 'L' or 'l', the leading ( k + 1 )
88 *> by n part of the array A must contain the lower triangular
89 *> band part of the symmetric matrix, supplied column by
90 *> column, with the leading diagonal of the matrix in row 1 of
91 *> the array, the first sub-diagonal starting at position 1 in
92 *> row 2, and so on. The bottom right k by k triangle of the
93 *> array A is not referenced.
94 *> The following program segment will transfer the lower
95 *> triangular part of a symmetric band matrix from conventional
96 *> full matrix storage to band storage:
97 *>
98 *> DO 20, J = 1, N
99 *> M = 1 - J
100 *> DO 10, I = J, MIN( N, J + K )
101 *> A( M + I, J ) = matrix( I, J )
102 *> 10 CONTINUE
103 *> 20 CONTINUE
104 *>
105 *> Unchanged on exit.
106 *>
107 *> LDA - INTEGER
108 *> On entry, LDA specifies the first dimension of A as declared
109 *> in the calling (sub) program. LDA must be at least
110 *> ( k + 1 ).
111 *> Unchanged on exit.
112 *>
113 *> X - COMPLEX array, dimension at least
114 *> ( 1 + ( N - 1 )*abs( INCX ) ).
115 *> Before entry, the incremented array X must contain the
116 *> vector x.
117 *> Unchanged on exit.
118 *>
119 *> INCX - INTEGER
120 *> On entry, INCX specifies the increment for the elements of
121 *> X. INCX must not be zero.
122 *> Unchanged on exit.
123 *>
124 *> BETA - COMPLEX
125 *> On entry, BETA specifies the scalar beta.
126 *> Unchanged on exit.
127 *>
128 *> Y - COMPLEX array, dimension at least
129 *> ( 1 + ( N - 1 )*abs( INCY ) ).
130 *> Before entry, the incremented array Y must contain the
131 *> vector y. On exit, Y is overwritten by the updated vector y.
132 *>
133 *> INCY - 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 *> \date November 2011
148 *
149 *> \ingroup complex_eig
150 *
151 * =====================================================================
152  SUBROUTINE csbmv( UPLO, N, K, ALPHA, A, LDA, X, INCX, BETA, Y,
153  $ incy )
154 *
155 * -- LAPACK test routine (version 3.4.0) --
156 * -- LAPACK is a software package provided by Univ. of Tennessee, --
157 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
158 * November 2011
159 *
160 * .. Scalar Arguments ..
161  CHARACTER uplo
162  INTEGER incx, incy, k, lda, n
163  COMPLEX alpha, beta
164 * ..
165 * .. Array Arguments ..
166  COMPLEX a( lda, * ), x( * ), y( * )
167 * ..
168 *
169 * =====================================================================
170 *
171 * .. Parameters ..
172  COMPLEX one
173  parameter( one = ( 1.0e+0, 0.0e+0 ) )
174  COMPLEX zero
175  parameter( zero = ( 0.0e+0, 0.0e+0 ) )
176 * ..
177 * .. Local Scalars ..
178  INTEGER i, info, ix, iy, j, jx, jy, kplus1, kx, ky, l
179  COMPLEX temp1, temp2
180 * ..
181 * .. External Functions ..
182  LOGICAL lsame
183  EXTERNAL lsame
184 * ..
185 * .. External Subroutines ..
186  EXTERNAL xerbla
187 * ..
188 * .. Intrinsic Functions ..
189  INTRINSIC max, min
190 * ..
191 * .. Executable Statements ..
192 *
193 * Test the input parameters.
194 *
195  info = 0
196  IF( .NOT.lsame( uplo, 'U' ) .AND. .NOT.lsame( uplo, 'L' ) ) THEN
197  info = 1
198  ELSE IF( n.LT.0 ) THEN
199  info = 2
200  ELSE IF( k.LT.0 ) THEN
201  info = 3
202  ELSE IF( lda.LT.( k+1 ) ) THEN
203  info = 6
204  ELSE IF( incx.EQ.0 ) THEN
205  info = 8
206  ELSE IF( incy.EQ.0 ) THEN
207  info = 11
208  END IF
209  IF( info.NE.0 ) THEN
210  CALL xerbla( 'CSBMV ', info )
211  RETURN
212  END IF
213 *
214 * Quick return if possible.
215 *
216  IF( ( n.EQ.0 ) .OR. ( ( alpha.EQ.zero ) .AND. ( beta.EQ.one ) ) )
217  $ RETURN
218 *
219 * Set up the start points in X and Y.
220 *
221  IF( incx.GT.0 ) THEN
222  kx = 1
223  ELSE
224  kx = 1 - ( n-1 )*incx
225  END IF
226  IF( incy.GT.0 ) THEN
227  ky = 1
228  ELSE
229  ky = 1 - ( n-1 )*incy
230  END IF
231 *
232 * Start the operations. In this version the elements of the array A
233 * are accessed sequentially with one pass through A.
234 *
235 * First form y := beta*y.
236 *
237  IF( beta.NE.one ) THEN
238  IF( incy.EQ.1 ) THEN
239  IF( beta.EQ.zero ) THEN
240  DO 10 i = 1, n
241  y( i ) = zero
242  10 CONTINUE
243  ELSE
244  DO 20 i = 1, n
245  y( i ) = beta*y( i )
246  20 CONTINUE
247  END IF
248  ELSE
249  iy = ky
250  IF( beta.EQ.zero ) THEN
251  DO 30 i = 1, n
252  y( iy ) = zero
253  iy = iy + incy
254  30 CONTINUE
255  ELSE
256  DO 40 i = 1, n
257  y( iy ) = beta*y( iy )
258  iy = iy + incy
259  40 CONTINUE
260  END IF
261  END IF
262  END IF
263  IF( alpha.EQ.zero )
264  $ RETURN
265  IF( lsame( uplo, 'U' ) ) THEN
266 *
267 * Form y when upper triangle of A is stored.
268 *
269  kplus1 = k + 1
270  IF( ( incx.EQ.1 ) .AND. ( incy.EQ.1 ) ) THEN
271  DO 60 j = 1, n
272  temp1 = alpha*x( j )
273  temp2 = zero
274  l = kplus1 - j
275  DO 50 i = max( 1, j-k ), j - 1
276  y( i ) = y( i ) + temp1*a( l+i, j )
277  temp2 = temp2 + a( l+i, j )*x( i )
278  50 CONTINUE
279  y( j ) = y( j ) + temp1*a( kplus1, j ) + alpha*temp2
280  60 CONTINUE
281  ELSE
282  jx = kx
283  jy = ky
284  DO 80 j = 1, n
285  temp1 = alpha*x( jx )
286  temp2 = zero
287  ix = kx
288  iy = ky
289  l = kplus1 - j
290  DO 70 i = max( 1, j-k ), j - 1
291  y( iy ) = y( iy ) + temp1*a( l+i, j )
292  temp2 = temp2 + a( l+i, j )*x( ix )
293  ix = ix + incx
294  iy = iy + incy
295  70 CONTINUE
296  y( jy ) = y( jy ) + temp1*a( kplus1, j ) + alpha*temp2
297  jx = jx + incx
298  jy = jy + incy
299  IF( j.GT.k ) THEN
300  kx = kx + incx
301  ky = ky + incy
302  END IF
303  80 CONTINUE
304  END IF
305  ELSE
306 *
307 * Form y when lower triangle of A is stored.
308 *
309  IF( ( incx.EQ.1 ) .AND. ( incy.EQ.1 ) ) THEN
310  DO 100 j = 1, n
311  temp1 = alpha*x( j )
312  temp2 = zero
313  y( j ) = y( j ) + temp1*a( 1, j )
314  l = 1 - j
315  DO 90 i = j + 1, min( n, j+k )
316  y( i ) = y( i ) + temp1*a( l+i, j )
317  temp2 = temp2 + a( l+i, j )*x( i )
318  90 CONTINUE
319  y( j ) = y( j ) + alpha*temp2
320  100 CONTINUE
321  ELSE
322  jx = kx
323  jy = ky
324  DO 120 j = 1, n
325  temp1 = alpha*x( jx )
326  temp2 = zero
327  y( jy ) = y( jy ) + temp1*a( 1, j )
328  l = 1 - j
329  ix = jx
330  iy = jy
331  DO 110 i = j + 1, min( n, j+k )
332  ix = ix + incx
333  iy = iy + incy
334  y( iy ) = y( iy ) + temp1*a( l+i, j )
335  temp2 = temp2 + a( l+i, j )*x( ix )
336  110 CONTINUE
337  y( jy ) = y( jy ) + alpha*temp2
338  jx = jx + incx
339  jy = jy + incy
340  120 CONTINUE
341  END IF
342  END IF
343 *
344  RETURN
345 *
346 * End of CSBMV
347 *
348  END