SUBROUTINE DLARGV( N, X, INCX, Y, INCY, C, INCC ) * * -- LAPACK auxiliary routine (version 3.2) -- * -- LAPACK is a software package provided by Univ. of Tennessee, -- * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- * November 2006 * * .. Scalar Arguments .. INTEGER INCC, INCX, INCY, N * .. * .. Array Arguments .. DOUBLE PRECISION C( * ), X( * ), Y( * ) * .. * * Purpose * ======= * * DLARGV generates a vector of real plane rotations, determined by * elements of the real vectors x and y. For i = 1,2,...,n * * ( c(i) s(i) ) ( x(i) ) = ( a(i) ) * ( -s(i) c(i) ) ( y(i) ) = ( 0 ) * * Arguments * ========= * * N (input) INTEGER * The number of plane rotations to be generated. * * X (input/output) DOUBLE PRECISION array, * dimension (1+(N-1)*INCX) * On entry, the vector x. * On exit, x(i) is overwritten by a(i), for i = 1,...,n. * * INCX (input) INTEGER * The increment between elements of X. INCX > 0. * * Y (input/output) DOUBLE PRECISION array, * dimension (1+(N-1)*INCY) * On entry, the vector y. * On exit, the sines of the plane rotations. * * INCY (input) INTEGER * The increment between elements of Y. INCY > 0. * * C (output) DOUBLE PRECISION array, dimension (1+(N-1)*INCC) * The cosines of the plane rotations. * * INCC (input) INTEGER * The increment between elements of C. INCC > 0. * * ===================================================================== * * .. Parameters .. DOUBLE PRECISION ZERO, ONE PARAMETER ( ZERO = 0.0D+0, ONE = 1.0D+0 ) * .. * .. Local Scalars .. INTEGER I, IC, IX, IY DOUBLE PRECISION F, G, T, TT * .. * .. Intrinsic Functions .. INTRINSIC ABS, SQRT * .. * .. Executable Statements .. * IX = 1 IY = 1 IC = 1 DO 10 I = 1, N F = X( IX ) G = Y( IY ) IF( G.EQ.ZERO ) THEN C( IC ) = ONE ELSE IF( F.EQ.ZERO ) THEN C( IC ) = ZERO Y( IY ) = ONE X( IX ) = G ELSE IF( ABS( F ).GT.ABS( G ) ) THEN T = G / F TT = SQRT( ONE+T*T ) C( IC ) = ONE / TT Y( IY ) = T*C( IC ) X( IX ) = F*TT ELSE T = F / G TT = SQRT( ONE+T*T ) Y( IY ) = ONE / TT C( IC ) = T*Y( IY ) X( IX ) = G*TT END IF IC = IC + INCC IY = IY + INCY IX = IX + INCX 10 CONTINUE RETURN * * End of DLARGV * END