3 * =========== DOCUMENTATION ===========
5 * Online html documentation available at
6 * http://www.netlib.org/lapack/explore-html/
11 * SUBROUTINE SSBMV(UPLO,N,K,ALPHA,A,LDA,X,INCX,BETA,Y,INCY)
13 * .. Scalar Arguments ..
15 * INTEGER INCX,INCY,K,LDA,N
18 * .. Array Arguments ..
19 * REAL A(LDA,*),X(*),Y(*)
28 *> SSBMV performs the matrix-vector operation
30 *> y := alpha*A*x + beta*y,
32 *> where alpha and beta are scalars, x and y are n element vectors and
33 *> A is an n by n symmetric band matrix, with k super-diagonals.
41 *> UPLO is CHARACTER*1
42 *> On entry, UPLO specifies whether the upper or lower
43 *> triangular part of the band matrix A is being supplied as
46 *> UPLO = 'U' or 'u' The upper triangular part of A is
49 *> UPLO = 'L' or 'l' The lower triangular part of A is
56 *> On entry, N specifies the order of the matrix A.
57 *> N must be at least zero.
63 *> On entry, K specifies the number of super-diagonals of the
64 *> matrix A. K must satisfy 0 .le. K.
70 *> On entry, ALPHA specifies the scalar alpha.
75 *> A is REAL array of DIMENSION ( LDA, n ).
76 *> Before entry with UPLO = 'U' or 'u', the leading ( k + 1 )
77 *> by n part of the array A must contain the upper triangular
78 *> band part of the symmetric matrix, supplied column by
79 *> column, with the leading diagonal of the matrix in row
80 *> ( k + 1 ) of the array, the first super-diagonal starting at
81 *> position 2 in row k, and so on. The top left k by k triangle
82 *> of the array A is not referenced.
83 *> The following program segment will transfer the upper
84 *> triangular part of a symmetric band matrix from conventional
85 *> full matrix storage to band storage:
89 *> DO 10, I = MAX( 1, J - K ), J
90 *> A( M + I, J ) = matrix( I, J )
94 *> Before entry with UPLO = 'L' or 'l', the leading ( k + 1 )
95 *> by n part of the array A must contain the lower triangular
96 *> band part of the symmetric matrix, supplied column by
97 *> column, with the leading diagonal of the matrix in row 1 of
98 *> the array, the first sub-diagonal starting at position 1 in
99 *> row 2, and so on. The bottom right k by k triangle of the
100 *> array A is not referenced.
101 *> The following program segment will transfer the lower
102 *> triangular part of a symmetric band matrix from conventional
103 *> full matrix storage to band storage:
107 *> DO 10, I = J, MIN( N, J + K )
108 *> A( M + I, J ) = matrix( I, J )
116 *> On entry, LDA specifies the first dimension of A as declared
117 *> in the calling (sub) program. LDA must be at least
123 *> X is REAL array of DIMENSION at least
124 *> ( 1 + ( n - 1 )*abs( INCX ) ).
125 *> Before entry, the incremented array X must contain the
132 *> On entry, INCX specifies the increment for the elements of
133 *> X. INCX must not be zero.
139 *> On entry, BETA specifies the scalar beta.
144 *> Y is REAL array of DIMENSION at least
145 *> ( 1 + ( n - 1 )*abs( INCY ) ).
146 *> Before entry, the incremented array Y must contain the
147 *> vector y. On exit, Y is overwritten by the updated vector y.
153 *> On entry, INCY specifies the increment for the elements of
154 *> Y. INCY must not be zero.
160 *> \author Univ. of Tennessee
161 *> \author Univ. of California Berkeley
162 *> \author Univ. of Colorado Denver
165 *> \date November 2011
167 *> \ingroup single_blas_level2
169 *> \par Further Details:
170 * =====================
174 *> Level 2 Blas routine.
175 *> The vector and matrix arguments are not referenced when N = 0, or M = 0
177 *> -- Written on 22-October-1986.
178 *> Jack Dongarra, Argonne National Lab.
179 *> Jeremy Du Croz, Nag Central Office.
180 *> Sven Hammarling, Nag Central Office.
181 *> Richard Hanson, Sandia National Labs.
184 * =====================================================================
185 SUBROUTINE SSBMV(UPLO,N,K,ALPHA,A,LDA,X,INCX,BETA,Y,INCY)
187 * -- Reference BLAS level2 routine (version 3.4.0) --
188 * -- Reference BLAS is a software package provided by Univ. of Tennessee, --
189 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
192 * .. Scalar Arguments ..
194 INTEGER INCX,INCY,K,LDA,N
197 * .. Array Arguments ..
198 REAL A(LDA,*),X(*),Y(*)
201 * =====================================================================
205 PARAMETER (ONE=1.0E+0,ZERO=0.0E+0)
207 * .. Local Scalars ..
209 INTEGER I,INFO,IX,IY,J,JX,JY,KPLUS1,KX,KY,L
211 * .. External Functions ..
215 * .. External Subroutines ..
218 * .. Intrinsic Functions ..
222 * Test the input parameters.
225 IF (.NOT.LSAME(UPLO,'U') .AND. .NOT.LSAME(UPLO,'L')) THEN
227 ELSE IF (N.LT.0) THEN
229 ELSE IF (K.LT.0) THEN
231 ELSE IF (LDA.LT. (K+1)) THEN
233 ELSE IF (INCX.EQ.0) THEN
235 ELSE IF (INCY.EQ.0) THEN
239 CALL XERBLA('SSBMV ',INFO)
243 * Quick return if possible.
245 IF ((N.EQ.0) .OR. ((ALPHA.EQ.ZERO).AND. (BETA.EQ.ONE))) RETURN
247 * Set up the start points in X and Y.
260 * Start the operations. In this version the elements of the array A
261 * are accessed sequentially with one pass through A.
263 * First form y := beta*y.
265 IF (BETA.NE.ONE) THEN
267 IF (BETA.EQ.ZERO) THEN
278 IF (BETA.EQ.ZERO) THEN
291 IF (ALPHA.EQ.ZERO) RETURN
292 IF (LSAME(UPLO,'U')) THEN
294 * Form y when upper triangle of A is stored.
297 IF ((INCX.EQ.1) .AND. (INCY.EQ.1)) THEN
302 DO 50 I = MAX(1,J-K),J - 1
303 Y(I) = Y(I) + TEMP1*A(L+I,J)
304 TEMP2 = TEMP2 + A(L+I,J)*X(I)
306 Y(J) = Y(J) + TEMP1*A(KPLUS1,J) + ALPHA*TEMP2
317 DO 70 I = MAX(1,J-K),J - 1
318 Y(IY) = Y(IY) + TEMP1*A(L+I,J)
319 TEMP2 = TEMP2 + A(L+I,J)*X(IX)
323 Y(JY) = Y(JY) + TEMP1*A(KPLUS1,J) + ALPHA*TEMP2
334 * Form y when lower triangle of A is stored.
336 IF ((INCX.EQ.1) .AND. (INCY.EQ.1)) THEN
340 Y(J) = Y(J) + TEMP1*A(1,J)
342 DO 90 I = J + 1,MIN(N,J+K)
343 Y(I) = Y(I) + TEMP1*A(L+I,J)
344 TEMP2 = TEMP2 + A(L+I,J)*X(I)
346 Y(J) = Y(J) + ALPHA*TEMP2
354 Y(JY) = Y(JY) + TEMP1*A(1,J)
358 DO 110 I = J + 1,MIN(N,J+K)
361 Y(IY) = Y(IY) + TEMP1*A(L+I,J)
362 TEMP2 = TEMP2 + A(L+I,J)*X(IX)
364 Y(JY) = Y(JY) + ALPHA*TEMP2