* ************************************************************************ * SUBROUTINE ECHER2( UPLO, N, ALPHA, X, INCX, Y, INCY, A, LDA ) * .. Scalar Arguments .. COMPLEX ALPHA INTEGER INCX, INCY, LDA, N CHARACTER*1 UPLO * .. Array Arguments .. COMPLEX*16 X( * ), Y( * ) COMPLEX A( LDA, * ) * .. * * Purpose * ======= * * ECHER2 performs the hermitian rank 2 operation * * A := alpha*x*conjg( y' ) + conjg( alpha )*y*conjg( x' ) + A, * * where alpha is a scalar, x and y are n element vectors and A is an n * by n hermitian matrix. Additional precision arithmetic is used in the * computation. * * Parameters * ========== * * UPLO - 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 - INTEGER. * On entry, N specifies the order of the matrix A. * N must be at least zero. * Unchanged on exit. * * ALPHA - COMPLEX . * On entry, ALPHA specifies the scalar alpha. * Unchanged on exit. * * X - COMPLEX*16 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. * * Y - COMPLEX*16 array of dimension at least * ( 1 + ( n - 1 )*abs( INCY ) ). * Before entry, the incremented array Y must contain the n * element vector y. * Unchanged on exit. * * INCY - INTEGER. * On entry, INCY specifies the increment for the elements of * Y. INCY must not be zero. * Unchanged on exit. * * A - COMPLEX array of 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 hermitian matrix and the strictly * lower triangular part of A is not referenced. On exit, the * upper triangular part of the array A is overwritten by the * upper triangular part of the updated matrix. * 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 hermitian matrix and the strictly * upper triangular part of A is not referenced. On exit, the * lower triangular part of the array A is overwritten by the * lower triangular part of the updated matrix. * Note that the imaginary parts of the diagonal elements need * not be set, they are assumed to be zero, and on exit they * are set to zero. At least double precision arithmetic is * used in the computation of A. * * LDA - 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. * * * Level 2 Blas routine. * * -- Written on 20-July-1986. * Sven Hammarling, Nag Central Office. * Richard Hanson, Sandia National Labs. * * * .. Parameters .. COMPLEX*16 ZERO PARAMETER ( ZERO = ( 0.0D+0, 0.0D+0 ) ) * .. Local Scalars .. COMPLEX*16 TEMP1, TEMP2 INTEGER I, INFO, IX, IY, J, JX, JY, KX, KY * .. External Functions .. LOGICAL LSAME EXTERNAL LSAME * .. External Subroutines .. EXTERNAL XERBLA * .. Intrinsic Functions .. INTRINSIC DCONJG, DBLE, CMPLX, MAX, REAL * .. * .. 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 ( INCX.EQ.0 ) THEN INFO = 5 ELSE IF ( INCY.EQ.0 ) THEN INFO = 7 ELSE IF ( LDA.LT.MAX(1,N) ) THEN INFO = 9 END IF IF( INFO.NE.0 )THEN CALL XERBLA( 'ECHER2', INFO ) RETURN END IF * * Quick return if possible. * IF( ( N.EQ.0 ).OR.( ALPHA.EQ.CMPLX( ZERO ) ) ) \$ RETURN * * Set up the start points in X and Y if the increments are not both * unity. * IF( ( INCX.NE.1 ).OR.( INCY.NE.1 ) )THEN 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 END IF * * Start the operations. In this version the elements of A are * accessed sequentially with one pass through the triangular part * of A. * IF( LSAME( UPLO, 'U' ) )THEN * * Form A when A is stored in the upper triangle. * IF( ( INCX.EQ.1 ).AND.( INCY.EQ.1 ) )THEN DO 20, J = 1, N IF( ( X( J ).NE.ZERO ).OR.( Y( J ).NE.ZERO ) )THEN TEMP1 = ALPHA*DCONJG( Y( J ) ) TEMP2 = DCONJG( ALPHA*X( J ) ) DO 10, I = 1, J - 1 A( I, J ) = A( I, J ) + X( I )*TEMP1 + Y( I )*TEMP2 10 CONTINUE A( J, J ) = REAL( A( J, J ) ) + \$ DBLE( X( J )*TEMP1 + Y( J )*TEMP2 ) ELSE A( J, J ) = REAL( A( J, J ) ) END IF 20 CONTINUE ELSE JX = KX JY = KY DO 40, J = 1, N IF( ( X( JX ).NE.ZERO ).OR.( Y( JY ).NE.ZERO ) )THEN TEMP1 = ALPHA*DCONJG( Y( JY ) ) TEMP2 = DCONJG( ALPHA*X( JX ) ) IX = KX IY = KY DO 30, I = 1, J - 1 A( I, J ) = A( I, J ) + X( IX )*TEMP1 \$ + Y( IY )*TEMP2 IX = IX + INCX IY = IY + INCY 30 CONTINUE A( J, J ) = REAL( A( J, J ) ) + \$ DBLE( X( JX )*TEMP1 + Y( JY )*TEMP2 ) ELSE A( J, J ) = REAL( A( J, J ) ) END IF JX = JX + INCX JY = JY + INCY 40 CONTINUE END IF ELSE * * Form A when A is stored in the lower triangle. * IF( ( INCX.EQ.1 ).AND.( INCY.EQ.1 ) )THEN DO 60, J = 1, N IF( ( X( J ).NE.ZERO ).OR.( Y( J ).NE.ZERO ) )THEN TEMP1 = ALPHA*DCONJG( Y( J ) ) TEMP2 = DCONJG( ALPHA*X( J ) ) A( J, J ) = REAL( A( J, J ) ) + \$ DBLE( X( J )*TEMP1 + Y( J )*TEMP2 ) DO 50, I = J + 1, N A( I, J ) = A( I, J ) + X( I )*TEMP1 + Y( I )*TEMP2 50 CONTINUE ELSE A( J, J ) = REAL( A( J, J ) ) END IF 60 CONTINUE ELSE JX = KX JY = KY DO 80, J = 1, N IF( ( X( JX ).NE.ZERO ).OR.( Y( JY ).NE.ZERO ) )THEN TEMP1 = ALPHA*DCONJG( Y( JY ) ) TEMP2 = DCONJG( ALPHA*X( JX ) ) A( J, J ) = REAL( A( J, J ) ) + \$ DBLE( X( JX )*TEMP1 + Y( JY )*TEMP2 ) IX = JX IY = JY DO 70, I = J + 1, N IX = IX + INCX IY = IY + INCY A( I, J ) = A( I, J ) + X( IX )*TEMP1 \$ + Y( IY )*TEMP2 70 CONTINUE ELSE A( J, J ) = REAL( A( J, J ) ) END IF JX = JX + INCX JY = JY + INCY 80 CONTINUE END IF END IF * RETURN * * End of ECHER2. * END