Annotation of rpl/lapack/lapack/dlargv.f, revision 1.1
1.1 ! bertrand 1: SUBROUTINE DLARGV( N, X, INCX, Y, INCY, C, INCC )
! 2: *
! 3: * -- LAPACK auxiliary routine (version 3.2) --
! 4: * -- LAPACK is a software package provided by Univ. of Tennessee, --
! 5: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
! 6: * November 2006
! 7: *
! 8: * .. Scalar Arguments ..
! 9: INTEGER INCC, INCX, INCY, N
! 10: * ..
! 11: * .. Array Arguments ..
! 12: DOUBLE PRECISION C( * ), X( * ), Y( * )
! 13: * ..
! 14: *
! 15: * Purpose
! 16: * =======
! 17: *
! 18: * DLARGV generates a vector of real plane rotations, determined by
! 19: * elements of the real vectors x and y. For i = 1,2,...,n
! 20: *
! 21: * ( c(i) s(i) ) ( x(i) ) = ( a(i) )
! 22: * ( -s(i) c(i) ) ( y(i) ) = ( 0 )
! 23: *
! 24: * Arguments
! 25: * =========
! 26: *
! 27: * N (input) INTEGER
! 28: * The number of plane rotations to be generated.
! 29: *
! 30: * X (input/output) DOUBLE PRECISION array,
! 31: * dimension (1+(N-1)*INCX)
! 32: * On entry, the vector x.
! 33: * On exit, x(i) is overwritten by a(i), for i = 1,...,n.
! 34: *
! 35: * INCX (input) INTEGER
! 36: * The increment between elements of X. INCX > 0.
! 37: *
! 38: * Y (input/output) DOUBLE PRECISION array,
! 39: * dimension (1+(N-1)*INCY)
! 40: * On entry, the vector y.
! 41: * On exit, the sines of the plane rotations.
! 42: *
! 43: * INCY (input) INTEGER
! 44: * The increment between elements of Y. INCY > 0.
! 45: *
! 46: * C (output) DOUBLE PRECISION array, dimension (1+(N-1)*INCC)
! 47: * The cosines of the plane rotations.
! 48: *
! 49: * INCC (input) INTEGER
! 50: * The increment between elements of C. INCC > 0.
! 51: *
! 52: * =====================================================================
! 53: *
! 54: * .. Parameters ..
! 55: DOUBLE PRECISION ZERO, ONE
! 56: PARAMETER ( ZERO = 0.0D+0, ONE = 1.0D+0 )
! 57: * ..
! 58: * .. Local Scalars ..
! 59: INTEGER I, IC, IX, IY
! 60: DOUBLE PRECISION F, G, T, TT
! 61: * ..
! 62: * .. Intrinsic Functions ..
! 63: INTRINSIC ABS, SQRT
! 64: * ..
! 65: * .. Executable Statements ..
! 66: *
! 67: IX = 1
! 68: IY = 1
! 69: IC = 1
! 70: DO 10 I = 1, N
! 71: F = X( IX )
! 72: G = Y( IY )
! 73: IF( G.EQ.ZERO ) THEN
! 74: C( IC ) = ONE
! 75: ELSE IF( F.EQ.ZERO ) THEN
! 76: C( IC ) = ZERO
! 77: Y( IY ) = ONE
! 78: X( IX ) = G
! 79: ELSE IF( ABS( F ).GT.ABS( G ) ) THEN
! 80: T = G / F
! 81: TT = SQRT( ONE+T*T )
! 82: C( IC ) = ONE / TT
! 83: Y( IY ) = T*C( IC )
! 84: X( IX ) = F*TT
! 85: ELSE
! 86: T = F / G
! 87: TT = SQRT( ONE+T*T )
! 88: Y( IY ) = ONE / TT
! 89: C( IC ) = T*Y( IY )
! 90: X( IX ) = G*TT
! 91: END IF
! 92: IC = IC + INCC
! 93: IY = IY + INCY
! 94: IX = IX + INCX
! 95: 10 CONTINUE
! 96: RETURN
! 97: *
! 98: * End of DLARGV
! 99: *
! 100: END
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