Annotation of rpl/lapack/lapack/dlarrc.f, revision 1.1
1.1 ! bertrand 1: SUBROUTINE DLARRC( JOBT, N, VL, VU, D, E, PIVMIN,
! 2: $ EIGCNT, LCNT, RCNT, INFO )
! 3: *
! 4: * -- LAPACK auxiliary routine (version 3.2) --
! 5: * -- LAPACK is a software package provided by Univ. of Tennessee, --
! 6: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
! 7: * November 2006
! 8: *
! 9: * .. Scalar Arguments ..
! 10: CHARACTER JOBT
! 11: INTEGER EIGCNT, INFO, LCNT, N, RCNT
! 12: DOUBLE PRECISION PIVMIN, VL, VU
! 13: * ..
! 14: * .. Array Arguments ..
! 15: DOUBLE PRECISION D( * ), E( * )
! 16: * ..
! 17: *
! 18: * Purpose
! 19: * =======
! 20: *
! 21: * Find the number of eigenvalues of the symmetric tridiagonal matrix T
! 22: * that are in the interval (VL,VU] if JOBT = 'T', and of L D L^T
! 23: * if JOBT = 'L'.
! 24: *
! 25: * Arguments
! 26: * =========
! 27: *
! 28: * JOBT (input) CHARACTER*1
! 29: * = 'T': Compute Sturm count for matrix T.
! 30: * = 'L': Compute Sturm count for matrix L D L^T.
! 31: *
! 32: * N (input) INTEGER
! 33: * The order of the matrix. N > 0.
! 34: *
! 35: * VL (input) DOUBLE PRECISION
! 36: * VU (input) DOUBLE PRECISION
! 37: * The lower and upper bounds for the eigenvalues.
! 38: *
! 39: * D (input) DOUBLE PRECISION array, dimension (N)
! 40: * JOBT = 'T': The N diagonal elements of the tridiagonal matrix T.
! 41: * JOBT = 'L': The N diagonal elements of the diagonal matrix D.
! 42: *
! 43: * E (input) DOUBLE PRECISION array, dimension (N)
! 44: * JOBT = 'T': The N-1 offdiagonal elements of the matrix T.
! 45: * JOBT = 'L': The N-1 offdiagonal elements of the matrix L.
! 46: *
! 47: * PIVMIN (input) DOUBLE PRECISION
! 48: * The minimum pivot in the Sturm sequence for T.
! 49: *
! 50: * EIGCNT (output) INTEGER
! 51: * The number of eigenvalues of the symmetric tridiagonal matrix T
! 52: * that are in the interval (VL,VU]
! 53: *
! 54: * LCNT (output) INTEGER
! 55: * RCNT (output) INTEGER
! 56: * The left and right negcounts of the interval.
! 57: *
! 58: * INFO (output) INTEGER
! 59: *
! 60: * Further Details
! 61: * ===============
! 62: *
! 63: * Based on contributions by
! 64: * Beresford Parlett, University of California, Berkeley, USA
! 65: * Jim Demmel, University of California, Berkeley, USA
! 66: * Inderjit Dhillon, University of Texas, Austin, USA
! 67: * Osni Marques, LBNL/NERSC, USA
! 68: * Christof Voemel, University of California, Berkeley, USA
! 69: *
! 70: * =====================================================================
! 71: *
! 72: * .. Parameters ..
! 73: DOUBLE PRECISION ZERO
! 74: PARAMETER ( ZERO = 0.0D0 )
! 75: * ..
! 76: * .. Local Scalars ..
! 77: INTEGER I
! 78: LOGICAL MATT
! 79: DOUBLE PRECISION LPIVOT, RPIVOT, SL, SU, TMP, TMP2
! 80:
! 81: * ..
! 82: * .. External Functions ..
! 83: LOGICAL LSAME
! 84: EXTERNAL LSAME
! 85: * ..
! 86: * .. Executable Statements ..
! 87: *
! 88: INFO = 0
! 89: LCNT = 0
! 90: RCNT = 0
! 91: EIGCNT = 0
! 92: MATT = LSAME( JOBT, 'T' )
! 93:
! 94:
! 95: IF (MATT) THEN
! 96: * Sturm sequence count on T
! 97: LPIVOT = D( 1 ) - VL
! 98: RPIVOT = D( 1 ) - VU
! 99: IF( LPIVOT.LE.ZERO ) THEN
! 100: LCNT = LCNT + 1
! 101: ENDIF
! 102: IF( RPIVOT.LE.ZERO ) THEN
! 103: RCNT = RCNT + 1
! 104: ENDIF
! 105: DO 10 I = 1, N-1
! 106: TMP = E(I)**2
! 107: LPIVOT = ( D( I+1 )-VL ) - TMP/LPIVOT
! 108: RPIVOT = ( D( I+1 )-VU ) - TMP/RPIVOT
! 109: IF( LPIVOT.LE.ZERO ) THEN
! 110: LCNT = LCNT + 1
! 111: ENDIF
! 112: IF( RPIVOT.LE.ZERO ) THEN
! 113: RCNT = RCNT + 1
! 114: ENDIF
! 115: 10 CONTINUE
! 116: ELSE
! 117: * Sturm sequence count on L D L^T
! 118: SL = -VL
! 119: SU = -VU
! 120: DO 20 I = 1, N - 1
! 121: LPIVOT = D( I ) + SL
! 122: RPIVOT = D( I ) + SU
! 123: IF( LPIVOT.LE.ZERO ) THEN
! 124: LCNT = LCNT + 1
! 125: ENDIF
! 126: IF( RPIVOT.LE.ZERO ) THEN
! 127: RCNT = RCNT + 1
! 128: ENDIF
! 129: TMP = E(I) * D(I) * E(I)
! 130: *
! 131: TMP2 = TMP / LPIVOT
! 132: IF( TMP2.EQ.ZERO ) THEN
! 133: SL = TMP - VL
! 134: ELSE
! 135: SL = SL*TMP2 - VL
! 136: END IF
! 137: *
! 138: TMP2 = TMP / RPIVOT
! 139: IF( TMP2.EQ.ZERO ) THEN
! 140: SU = TMP - VU
! 141: ELSE
! 142: SU = SU*TMP2 - VU
! 143: END IF
! 144: 20 CONTINUE
! 145: LPIVOT = D( N ) + SL
! 146: RPIVOT = D( N ) + SU
! 147: IF( LPIVOT.LE.ZERO ) THEN
! 148: LCNT = LCNT + 1
! 149: ENDIF
! 150: IF( RPIVOT.LE.ZERO ) THEN
! 151: RCNT = RCNT + 1
! 152: ENDIF
! 153: ENDIF
! 154: EIGCNT = RCNT - LCNT
! 155:
! 156: RETURN
! 157: *
! 158: * end of DLARRC
! 159: *
! 160: END
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