| SUBROUTINE SSBMV(UPLO,N,K,ALPHA,A,LDA,X,INCX,BETA,Y,INCY) |
| * .. Scalar Arguments .. |
| REAL ALPHA,BETA |
| INTEGER INCX,INCY,K,LDA,N |
| CHARACTER UPLO |
| * .. |
| * .. Array Arguments .. |
| REAL A(LDA,*),X(*),Y(*) |
| * .. |
| * |
| * Purpose |
| * ======= |
| * |
| * SSBMV 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. |
| * |
| * Arguments |
| * ========== |
| * |
| * UPLO - 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. |
| * |
| * Unchanged on exit. |
| * |
| * N - INTEGER. |
| * On entry, N specifies the order of the matrix A. |
| * N must be at least zero. |
| * Unchanged on exit. |
| * |
| * K - INTEGER. |
| * On entry, K specifies the number of super-diagonals of the |
| * matrix A. K must satisfy 0 .le. K. |
| * Unchanged on exit. |
| * |
| * ALPHA - REAL . |
| * On entry, ALPHA specifies the scalar alpha. |
| * Unchanged on exit. |
| * |
| * A - REAL array of 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 |
| * |
| * Unchanged on exit. |
| * |
| * LDA - INTEGER. |
| * On entry, LDA specifies the first dimension of A as declared |
| * in the calling (sub) program. LDA must be at least |
| * ( k + 1 ). |
| * Unchanged on exit. |
| * |
| * X - REAL array of DIMENSION at least |
| * ( 1 + ( n - 1 )*abs( INCX ) ). |
| * Before entry, the incremented array X must contain the |
| * vector x. |
| * Unchanged on exit. |
| * |
| * INCX - INTEGER. |
| * On entry, INCX specifies the increment for the elements of |
| * X. INCX must not be zero. |
| * Unchanged on exit. |
| * |
| * BETA - REAL . |
| * On entry, BETA specifies the scalar beta. |
| * Unchanged on exit. |
| * |
| * Y - REAL array of 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. |
| * |
| * INCY - INTEGER. |
| * On entry, INCY specifies the increment for the elements of |
| * Y. INCY must not be zero. |
| * Unchanged on exit. |
| * |
| * Further Details |
| * =============== |
| * |
| * Level 2 Blas routine. |
| * |
| * -- 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. |
| * |
| * ===================================================================== |
| * |
| * .. Parameters .. |
| REAL ONE,ZERO |
| PARAMETER (ONE=1.0E+0,ZERO=0.0E+0) |
| * .. |
| * .. Local Scalars .. |
| REAL 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('SSBMV ',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 SSBMV . |
| * |
| END |
