SUBROUTINE CSYMV( UPLO, N, ALPHA, A, LDA, X, INCX, BETA, Y, INCY ) * * -- LAPACK auxiliary routine (version 3.1) -- * Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. * November 2006 * * .. Scalar Arguments .. CHARACTER UPLO INTEGER INCX, INCY, LDA, N COMPLEX ALPHA, BETA * .. * .. Array Arguments .. COMPLEX A( LDA, * ), X( * ), Y( * ) * .. * * Purpose * ======= * * CSYMV 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. * * Arguments * ========== * * UPLO (input) CHARACTER*1 * On entry, UPLO specifies whether the upper or lower * triangular part of the array A is to be referenced as * follows: * * UPLO = 'U' or 'u' Only the upper triangular part of A * is to be referenced. * * UPLO = 'L' or 'l' Only the lower triangular part of A * is to be referenced. * * Unchanged on exit. * * N (input) INTEGER * On entry, N specifies the order of the matrix A. * N must be at least zero. * Unchanged on exit. * * ALPHA (input) COMPLEX * On entry, ALPHA specifies the scalar alpha. * Unchanged on exit. * * A (input) COMPLEX array, dimension ( LDA, N ) * Before entry, with UPLO = 'U' or 'u', the leading n by n * upper triangular part of the array A must contain the upper * triangular part of the symmetric matrix and the strictly * lower triangular part of A is not referenced. * Before entry, with UPLO = 'L' or 'l', the leading n by n * lower triangular part of the array A must contain the lower * triangular part of the symmetric matrix and the strictly * upper triangular part of A is not referenced. * Unchanged on exit. * * LDA (input) INTEGER * On entry, LDA specifies the first dimension of A as declared * in the calling (sub) program. LDA must be at least * max( 1, N ). * Unchanged on exit. * * X (input) COMPLEX array, 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 (input) INTEGER * On entry, INCX specifies the increment for the elements of * X. INCX must not be zero. * Unchanged on exit. * * BETA (input) COMPLEX * 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 (input/output) COMPLEX array, 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 (input) INTEGER * On entry, INCY specifies the increment for the elements of * Y. INCY must not be zero. * Unchanged on exit. * * ===================================================================== * * .. Parameters .. COMPLEX ONE PARAMETER ( ONE = ( 1.0E+0, 0.0E+0 ) ) COMPLEX ZERO PARAMETER ( ZERO = ( 0.0E+0, 0.0E+0 ) ) * .. * .. Local Scalars .. INTEGER I, INFO, IX, IY, J, JX, JY, KX, KY COMPLEX TEMP1, TEMP2 * .. * .. External Functions .. LOGICAL LSAME EXTERNAL LSAME * .. * .. External Subroutines .. EXTERNAL XERBLA * .. * .. Intrinsic Functions .. INTRINSIC MAX * .. * .. Executable Statements .. * * 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( LDA.LT.MAX( 1, N ) ) THEN INFO = 5 ELSE IF( INCX.EQ.0 ) THEN INFO = 7 ELSE IF( INCY.EQ.0 ) THEN INFO = 10 END IF IF( INFO.NE.0 ) THEN CALL XERBLA( 'CSYMV ', 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 A are * accessed sequentially with one pass through the triangular part * of 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 A is stored in upper triangle. * IF( ( INCX.EQ.1 ) .AND. ( INCY.EQ.1 ) ) THEN DO 60 J = 1, N TEMP1 = ALPHA*X( J ) TEMP2 = ZERO DO 50 I = 1, J - 1 Y( I ) = Y( I ) + TEMP1*A( I, J ) TEMP2 = TEMP2 + A( I, J )*X( I ) 50 CONTINUE Y( J ) = Y( J ) + TEMP1*A( J, 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 DO 70 I = 1, J - 1 Y( IY ) = Y( IY ) + TEMP1*A( I, J ) TEMP2 = TEMP2 + A( I, J )*X( IX ) IX = IX + INCX IY = IY + INCY 70 CONTINUE Y( JY ) = Y( JY ) + TEMP1*A( J, J ) + ALPHA*TEMP2 JX = JX + INCX JY = JY + INCY 80 CONTINUE END IF ELSE * * Form y when A is stored in 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*A( J, J ) DO 90 I = J + 1, N Y( I ) = Y( I ) + TEMP1*A( I, J ) TEMP2 = TEMP2 + A( 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( J, J ) IX = JX IY = JY DO 110 I = J + 1, N IX = IX + INCX IY = IY + INCY Y( IY ) = Y( IY ) + TEMP1*A( I, J ) TEMP2 = TEMP2 + A( 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 CSYMV * END