| SUBROUTINE SSPMV(UPLO,N,ALPHA,AP,X,INCX,BETA,Y,INCY) |
| * .. Scalar Arguments .. |
| REAL ALPHA,BETA |
| INTEGER INCX,INCY,N |
| CHARACTER UPLO |
| * .. |
| * .. Array Arguments .. |
| REAL AP(*),X(*),Y(*) |
| * .. |
| * |
| * Purpose |
| * ======= |
| * |
| * SSPMV 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 matrix, supplied in packed form. |
| * |
| * Arguments |
| * ========== |
| * |
| * UPLO - CHARACTER*1. |
| * On entry, UPLO specifies whether the upper or lower |
| * triangular part of the matrix A is supplied in the packed |
| * array AP as follows: |
| * |
| * UPLO = 'U' or 'u' The upper triangular part of A is |
| * supplied in AP. |
| * |
| * UPLO = 'L' or 'l' The lower triangular part of A is |
| * supplied in AP. |
| * |
| * Unchanged on exit. |
| * |
| * N - INTEGER. |
| * On entry, N specifies the order of the matrix A. |
| * N must be at least zero. |
| * Unchanged on exit. |
| * |
| * ALPHA - REAL . |
| * On entry, ALPHA specifies the scalar alpha. |
| * Unchanged on exit. |
| * |
| * AP - REAL array of DIMENSION at least |
| * ( ( n*( n + 1 ) )/2 ). |
| * Before entry with UPLO = 'U' or 'u', the array AP must |
| * contain the upper triangular part of the symmetric matrix |
| * packed sequentially, column by column, so that AP( 1 ) |
| * contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 1, 2 ) |
| * and a( 2, 2 ) respectively, and so on. |
| * Before entry with UPLO = 'L' or 'l', the array AP must |
| * contain the lower triangular part of the symmetric matrix |
| * packed sequentially, column by column, so that AP( 1 ) |
| * contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 2, 1 ) |
| * and a( 3, 1 ) respectively, and so on. |
| * Unchanged on exit. |
| * |
| * X - REAL array of dimension at least |
| * ( 1 + ( n - 1 )*abs( INCX ) ). |
| * Before entry, the incremented array X must contain the n |
| * element 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. When BETA is |
| * supplied as zero then Y need not be set on input. |
| * Unchanged on exit. |
| * |
| * Y - REAL array of dimension at least |
| * ( 1 + ( n - 1 )*abs( INCY ) ). |
| * Before entry, the incremented array Y must contain the n |
| * element 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,K,KK,KX,KY |
| * .. |
| * .. External Functions .. |
| LOGICAL LSAME |
| EXTERNAL LSAME |
| * .. |
| * .. External Subroutines .. |
| EXTERNAL XERBLA |
| * .. |
| * |
| * 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 (INCX.EQ.0) THEN |
| INFO = 6 |
| ELSE IF (INCY.EQ.0) THEN |
| INFO = 9 |
| END IF |
| IF (INFO.NE.0) THEN |
| CALL XERBLA('SSPMV ',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 AP |
| * are accessed sequentially with one pass through AP. |
| * |
| * 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 |
| KK = 1 |
| IF (LSAME(UPLO,'U')) THEN |
| * |
| * Form y when AP contains the upper triangle. |
| * |
| IF ((INCX.EQ.1) .AND. (INCY.EQ.1)) THEN |
| DO 60 J = 1,N |
| TEMP1 = ALPHA*X(J) |
| TEMP2 = ZERO |
| K = KK |
| DO 50 I = 1,J - 1 |
| Y(I) = Y(I) + TEMP1*AP(K) |
| TEMP2 = TEMP2 + AP(K)*X(I) |
| K = K + 1 |
| 50 CONTINUE |
| Y(J) = Y(J) + TEMP1*AP(KK+J-1) + ALPHA*TEMP2 |
| KK = KK + J |
| 60 CONTINUE |
| ELSE |
| JX = KX |
| JY = KY |
| DO 80 J = 1,N |
| TEMP1 = ALPHA*X(JX) |
| TEMP2 = ZERO |
| IX = KX |
| IY = KY |
| DO 70 K = KK,KK + J - 2 |
| Y(IY) = Y(IY) + TEMP1*AP(K) |
| TEMP2 = TEMP2 + AP(K)*X(IX) |
| IX = IX + INCX |
| IY = IY + INCY |
| 70 CONTINUE |
| Y(JY) = Y(JY) + TEMP1*AP(KK+J-1) + ALPHA*TEMP2 |
| JX = JX + INCX |
| JY = JY + INCY |
| KK = KK + J |
| 80 CONTINUE |
| END IF |
| ELSE |
| * |
| * Form y when AP contains the lower triangle. |
| * |
| 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*AP(KK) |
| K = KK + 1 |
| DO 90 I = J + 1,N |
| Y(I) = Y(I) + TEMP1*AP(K) |
| TEMP2 = TEMP2 + AP(K)*X(I) |
| K = K + 1 |
| 90 CONTINUE |
| Y(J) = Y(J) + ALPHA*TEMP2 |
| KK = KK + (N-J+1) |
| 100 CONTINUE |
| ELSE |
| JX = KX |
| JY = KY |
| DO 120 J = 1,N |
| TEMP1 = ALPHA*X(JX) |
| TEMP2 = ZERO |
| Y(JY) = Y(JY) + TEMP1*AP(KK) |
| IX = JX |
| IY = JY |
| DO 110 K = KK + 1,KK + N - J |
| IX = IX + INCX |
| IY = IY + INCY |
| Y(IY) = Y(IY) + TEMP1*AP(K) |
| TEMP2 = TEMP2 + AP(K)*X(IX) |
| 110 CONTINUE |
| Y(JY) = Y(JY) + ALPHA*TEMP2 |
| JX = JX + INCX |
| JY = JY + INCY |
| KK = KK + (N-J+1) |
| 120 CONTINUE |
| END IF |
| END IF |
| * |
| RETURN |
| * |
| * End of SSPMV . |
| * |
| END |
