*> \brief \b DSBMV * * =========== DOCUMENTATION =========== * * Online html documentation available at * http://www.netlib.org/lapack/explore-html/ * * Definition: * =========== * * SUBROUTINE DSBMV(UPLO,N,K,ALPHA,A,LDA,X,INCX,BETA,Y,INCY) * * .. Scalar Arguments .. * DOUBLE PRECISION ALPHA,BETA * INTEGER INCX,INCY,K,LDA,N * CHARACTER UPLO * .. * .. Array Arguments .. * DOUBLE PRECISION A(LDA,*),X(*),Y(*) * .. * * *> \par Purpose: * ============= *> *> \verbatim *> *> DSBMV performs the matrix-vector operation *> *> y := alpha*A*x + beta*y, *> *> where alpha and beta are scalars, x and y are n element vectors and *> A is an n by n symmetric band matrix, with k super-diagonals. *> \endverbatim * * Arguments: * ========== * *> \param[in] UPLO *> \verbatim *> UPLO is CHARACTER*1 *> On entry, UPLO specifies whether the upper or lower *> triangular part of the band matrix A is being supplied as *> follows: *> *> UPLO = 'U' or 'u' The upper triangular part of A is *> being supplied. *> *> UPLO = 'L' or 'l' The lower triangular part of A is *> being supplied. *> \endverbatim *> *> \param[in] N *> \verbatim *> N is INTEGER *> On entry, N specifies the order of the matrix A. *> N must be at least zero. *> \endverbatim *> *> \param[in] K *> \verbatim *> K is INTEGER *> On entry, K specifies the number of super-diagonals of the *> matrix A. K must satisfy 0 .le. K. *> \endverbatim *> *> \param[in] ALPHA *> \verbatim *> ALPHA is DOUBLE PRECISION. *> On entry, ALPHA specifies the scalar alpha. *> \endverbatim *> *> \param[in] A *> \verbatim *> A is DOUBLE PRECISION array, dimension ( LDA, N ) *> Before entry with UPLO = 'U' or 'u', the leading ( k + 1 ) *> by n part of the array A must contain the upper triangular *> band part of the symmetric matrix, supplied column by *> column, with the leading diagonal of the matrix in row *> ( k + 1 ) of the array, the first super-diagonal starting at *> position 2 in row k, and so on. The top left k by k triangle *> of the array A is not referenced. *> The following program segment will transfer the upper *> triangular part of a symmetric band matrix from conventional *> full matrix storage to band storage: *> *> DO 20, J = 1, N *> M = K + 1 - J *> DO 10, I = MAX( 1, J - K ), J *> A( M + I, J ) = matrix( I, J ) *> 10 CONTINUE *> 20 CONTINUE *> *> Before entry with UPLO = 'L' or 'l', the leading ( k + 1 ) *> by n part of the array A must contain the lower triangular *> band part of the symmetric matrix, supplied column by *> column, with the leading diagonal of the matrix in row 1 of *> the array, the first sub-diagonal starting at position 1 in *> row 2, and so on. The bottom right k by k triangle of the *> array A is not referenced. *> The following program segment will transfer the lower *> triangular part of a symmetric band matrix from conventional *> full matrix storage to band storage: *> *> DO 20, J = 1, N *> M = 1 - J *> DO 10, I = J, MIN( N, J + K ) *> A( M + I, J ) = matrix( I, J ) *> 10 CONTINUE *> 20 CONTINUE *> \endverbatim *> *> \param[in] LDA *> \verbatim *> LDA is INTEGER *> On entry, LDA specifies the first dimension of A as declared *> in the calling (sub) program. LDA must be at least *> ( k + 1 ). *> \endverbatim *> *> \param[in] X *> \verbatim *> X is DOUBLE PRECISION array, dimension at least *> ( 1 + ( n - 1 )*abs( INCX ) ). *> Before entry, the incremented array X must contain the *> vector x. *> \endverbatim *> *> \param[in] INCX *> \verbatim *> INCX is INTEGER *> On entry, INCX specifies the increment for the elements of *> X. INCX must not be zero. *> \endverbatim *> *> \param[in] BETA *> \verbatim *> BETA is DOUBLE PRECISION. *> On entry, BETA specifies the scalar beta. *> \endverbatim *> *> \param[in,out] Y *> \verbatim *> Y is DOUBLE PRECISION array, dimension at least *> ( 1 + ( n - 1 )*abs( INCY ) ). *> Before entry, the incremented array Y must contain the *> vector y. On exit, Y is overwritten by the updated vector y. *> \endverbatim *> *> \param[in] INCY *> \verbatim *> INCY is INTEGER *> On entry, INCY specifies the increment for the elements of *> Y. INCY must not be zero. *> \endverbatim * * Authors: * ======== * *> \author Univ. of Tennessee *> \author Univ. of California Berkeley *> \author Univ. of Colorado Denver *> \author NAG Ltd. * *> \ingroup double_blas_level2 * *> \par Further Details: * ===================== *> *> \verbatim *> *> Level 2 Blas routine. *> The vector and matrix arguments are not referenced when N = 0, or M = 0 *> *> -- Written on 22-October-1986. *> Jack Dongarra, Argonne National Lab. *> Jeremy Du Croz, Nag Central Office. *> Sven Hammarling, Nag Central Office. *> Richard Hanson, Sandia National Labs. *> \endverbatim *> * ===================================================================== SUBROUTINE DSBMV(UPLO,N,K,ALPHA,A,LDA,X,INCX,BETA,Y,INCY) * * -- Reference BLAS level2 routine -- * -- Reference BLAS is a software package provided by Univ. of Tennessee, -- * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- * * .. Scalar Arguments .. DOUBLE PRECISION ALPHA,BETA INTEGER INCX,INCY,K,LDA,N CHARACTER UPLO * .. * .. Array Arguments .. DOUBLE PRECISION A(LDA,*),X(*),Y(*) * .. * * ===================================================================== * * .. Parameters .. DOUBLE PRECISION ONE,ZERO PARAMETER (ONE=1.0D+0,ZERO=0.0D+0) * .. * .. Local Scalars .. DOUBLE PRECISION TEMP1,TEMP2 INTEGER I,INFO,IX,IY,J,JX,JY,KPLUS1,KX,KY,L * .. * .. External Functions .. LOGICAL LSAME EXTERNAL LSAME * .. * .. External Subroutines .. EXTERNAL XERBLA * .. * .. Intrinsic Functions .. INTRINSIC MAX,MIN * .. * * Test the input parameters. * INFO = 0 IF (.NOT.LSAME(UPLO,'U') .AND. .NOT.LSAME(UPLO,'L')) THEN INFO = 1 ELSE IF (N.LT.0) THEN INFO = 2 ELSE IF (K.LT.0) THEN INFO = 3 ELSE IF (LDA.LT. (K+1)) THEN INFO = 6 ELSE IF (INCX.EQ.0) THEN INFO = 8 ELSE IF (INCY.EQ.0) THEN INFO = 11 END IF IF (INFO.NE.0) THEN CALL XERBLA('DSBMV ',INFO) RETURN END IF * * Quick return if possible. * IF ((N.EQ.0) .OR. ((ALPHA.EQ.ZERO).AND. (BETA.EQ.ONE))) RETURN * * Set up the start points in X and Y. * IF (INCX.GT.0) THEN KX = 1 ELSE KX = 1 - (N-1)*INCX END IF IF (INCY.GT.0) THEN KY = 1 ELSE KY = 1 - (N-1)*INCY END IF * * Start the operations. In this version the elements of the array A * are accessed sequentially with one pass through A. * * First form y := beta*y. * IF (BETA.NE.ONE) THEN IF (INCY.EQ.1) THEN IF (BETA.EQ.ZERO) THEN DO 10 I = 1,N Y(I) = ZERO 10 CONTINUE ELSE DO 20 I = 1,N Y(I) = BETA*Y(I) 20 CONTINUE END IF ELSE IY = KY IF (BETA.EQ.ZERO) THEN DO 30 I = 1,N Y(IY) = ZERO IY = IY + INCY 30 CONTINUE ELSE DO 40 I = 1,N Y(IY) = BETA*Y(IY) IY = IY + INCY 40 CONTINUE END IF END IF END IF IF (ALPHA.EQ.ZERO) RETURN IF (LSAME(UPLO,'U')) THEN * * Form y when upper triangle of A is stored. * KPLUS1 = K + 1 IF ((INCX.EQ.1) .AND. (INCY.EQ.1)) THEN DO 60 J = 1,N TEMP1 = ALPHA*X(J) TEMP2 = ZERO L = KPLUS1 - J DO 50 I = MAX(1,J-K),J - 1 Y(I) = Y(I) + TEMP1*A(L+I,J) TEMP2 = TEMP2 + A(L+I,J)*X(I) 50 CONTINUE Y(J) = Y(J) + TEMP1*A(KPLUS1,J) + ALPHA*TEMP2 60 CONTINUE ELSE JX = KX JY = KY DO 80 J = 1,N TEMP1 = ALPHA*X(JX) TEMP2 = ZERO IX = KX IY = KY L = KPLUS1 - J DO 70 I = MAX(1,J-K),J - 1 Y(IY) = Y(IY) + TEMP1*A(L+I,J) TEMP2 = TEMP2 + A(L+I,J)*X(IX) IX = IX + INCX IY = IY + INCY 70 CONTINUE Y(JY) = Y(JY) + TEMP1*A(KPLUS1,J) + ALPHA*TEMP2 JX = JX + INCX JY = JY + INCY IF (J.GT.K) THEN KX = KX + INCX KY = KY + INCY END IF 80 CONTINUE END IF ELSE * * Form y when lower triangle of A is stored. * IF ((INCX.EQ.1) .AND. (INCY.EQ.1)) THEN DO 100 J = 1,N TEMP1 = ALPHA*X(J) TEMP2 = ZERO Y(J) = Y(J) + TEMP1*A(1,J) L = 1 - J DO 90 I = J + 1,MIN(N,J+K) Y(I) = Y(I) + TEMP1*A(L+I,J) TEMP2 = TEMP2 + A(L+I,J)*X(I) 90 CONTINUE Y(J) = Y(J) + ALPHA*TEMP2 100 CONTINUE ELSE JX = KX JY = KY DO 120 J = 1,N TEMP1 = ALPHA*X(JX) TEMP2 = ZERO Y(JY) = Y(JY) + TEMP1*A(1,J) L = 1 - J IX = JX IY = JY DO 110 I = J + 1,MIN(N,J+K) IX = IX + INCX IY = IY + INCY Y(IY) = Y(IY) + TEMP1*A(L+I,J) TEMP2 = TEMP2 + A(L+I,J)*X(IX) 110 CONTINUE Y(JY) = Y(JY) + ALPHA*TEMP2 JX = JX + INCX JY = JY + INCY 120 CONTINUE END IF END IF * RETURN * * End of DSBMV * END