Annotation of rpl/lapack/lapack/zstegr.f, revision 1.1
1.1 ! bertrand 1: SUBROUTINE ZSTEGR( JOBZ, RANGE, N, D, E, VL, VU, IL, IU,
! 2: $ ABSTOL, M, W, Z, LDZ, ISUPPZ, WORK, LWORK, IWORK,
! 3: $ LIWORK, INFO )
! 4:
! 5: IMPLICIT NONE
! 6: *
! 7: *
! 8: * -- LAPACK computational routine (version 3.2) --
! 9: * -- LAPACK is a software package provided by Univ. of Tennessee, --
! 10: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
! 11: * November 2006
! 12: *
! 13: * .. Scalar Arguments ..
! 14: CHARACTER JOBZ, RANGE
! 15: INTEGER IL, INFO, IU, LDZ, LIWORK, LWORK, M, N
! 16: DOUBLE PRECISION ABSTOL, VL, VU
! 17: * ..
! 18: * .. Array Arguments ..
! 19: INTEGER ISUPPZ( * ), IWORK( * )
! 20: DOUBLE PRECISION D( * ), E( * ), W( * ), WORK( * )
! 21: COMPLEX*16 Z( LDZ, * )
! 22: * ..
! 23: *
! 24: * Purpose
! 25: * =======
! 26: *
! 27: * ZSTEGR computes selected eigenvalues and, optionally, eigenvectors
! 28: * of a real symmetric tridiagonal matrix T. Any such unreduced matrix has
! 29: * a well defined set of pairwise different real eigenvalues, the corresponding
! 30: * real eigenvectors are pairwise orthogonal.
! 31: *
! 32: * The spectrum may be computed either completely or partially by specifying
! 33: * either an interval (VL,VU] or a range of indices IL:IU for the desired
! 34: * eigenvalues.
! 35: *
! 36: * ZSTEGR is a compatability wrapper around the improved ZSTEMR routine.
! 37: * See DSTEMR for further details.
! 38: *
! 39: * One important change is that the ABSTOL parameter no longer provides any
! 40: * benefit and hence is no longer used.
! 41: *
! 42: * Note : ZSTEGR and ZSTEMR work only on machines which follow
! 43: * IEEE-754 floating-point standard in their handling of infinities and
! 44: * NaNs. Normal execution may create these exceptiona values and hence
! 45: * may abort due to a floating point exception in environments which
! 46: * do not conform to the IEEE-754 standard.
! 47: *
! 48: * Arguments
! 49: * =========
! 50: *
! 51: * JOBZ (input) CHARACTER*1
! 52: * = 'N': Compute eigenvalues only;
! 53: * = 'V': Compute eigenvalues and eigenvectors.
! 54: *
! 55: * RANGE (input) CHARACTER*1
! 56: * = 'A': all eigenvalues will be found.
! 57: * = 'V': all eigenvalues in the half-open interval (VL,VU]
! 58: * will be found.
! 59: * = 'I': the IL-th through IU-th eigenvalues will be found.
! 60: *
! 61: * N (input) INTEGER
! 62: * The order of the matrix. N >= 0.
! 63: *
! 64: * D (input/output) DOUBLE PRECISION array, dimension (N)
! 65: * On entry, the N diagonal elements of the tridiagonal matrix
! 66: * T. On exit, D is overwritten.
! 67: *
! 68: * E (input/output) DOUBLE PRECISION array, dimension (N)
! 69: * On entry, the (N-1) subdiagonal elements of the tridiagonal
! 70: * matrix T in elements 1 to N-1 of E. E(N) need not be set on
! 71: * input, but is used internally as workspace.
! 72: * On exit, E is overwritten.
! 73: *
! 74: * VL (input) DOUBLE PRECISION
! 75: * VU (input) DOUBLE PRECISION
! 76: * If RANGE='V', the lower and upper bounds of the interval to
! 77: * be searched for eigenvalues. VL < VU.
! 78: * Not referenced if RANGE = 'A' or 'I'.
! 79: *
! 80: * IL (input) INTEGER
! 81: * IU (input) INTEGER
! 82: * If RANGE='I', the indices (in ascending order) of the
! 83: * smallest and largest eigenvalues to be returned.
! 84: * 1 <= IL <= IU <= N, if N > 0.
! 85: * Not referenced if RANGE = 'A' or 'V'.
! 86: *
! 87: * ABSTOL (input) DOUBLE PRECISION
! 88: * Unused. Was the absolute error tolerance for the
! 89: * eigenvalues/eigenvectors in previous versions.
! 90: *
! 91: * M (output) INTEGER
! 92: * The total number of eigenvalues found. 0 <= M <= N.
! 93: * If RANGE = 'A', M = N, and if RANGE = 'I', M = IU-IL+1.
! 94: *
! 95: * W (output) DOUBLE PRECISION array, dimension (N)
! 96: * The first M elements contain the selected eigenvalues in
! 97: * ascending order.
! 98: *
! 99: * Z (output) COMPLEX*16 array, dimension (LDZ, max(1,M) )
! 100: * If JOBZ = 'V', and if INFO = 0, then the first M columns of Z
! 101: * contain the orthonormal eigenvectors of the matrix T
! 102: * corresponding to the selected eigenvalues, with the i-th
! 103: * column of Z holding the eigenvector associated with W(i).
! 104: * If JOBZ = 'N', then Z is not referenced.
! 105: * Note: the user must ensure that at least max(1,M) columns are
! 106: * supplied in the array Z; if RANGE = 'V', the exact value of M
! 107: * is not known in advance and an upper bound must be used.
! 108: * Supplying N columns is always safe.
! 109: *
! 110: * LDZ (input) INTEGER
! 111: * The leading dimension of the array Z. LDZ >= 1, and if
! 112: * JOBZ = 'V', then LDZ >= max(1,N).
! 113: *
! 114: * ISUPPZ (output) INTEGER ARRAY, dimension ( 2*max(1,M) )
! 115: * The support of the eigenvectors in Z, i.e., the indices
! 116: * indicating the nonzero elements in Z. The i-th computed eigenvector
! 117: * is nonzero only in elements ISUPPZ( 2*i-1 ) through
! 118: * ISUPPZ( 2*i ). This is relevant in the case when the matrix
! 119: * is split. ISUPPZ is only accessed when JOBZ is 'V' and N > 0.
! 120: *
! 121: * WORK (workspace/output) DOUBLE PRECISION array, dimension (LWORK)
! 122: * On exit, if INFO = 0, WORK(1) returns the optimal
! 123: * (and minimal) LWORK.
! 124: *
! 125: * LWORK (input) INTEGER
! 126: * The dimension of the array WORK. LWORK >= max(1,18*N)
! 127: * if JOBZ = 'V', and LWORK >= max(1,12*N) if JOBZ = 'N'.
! 128: * If LWORK = -1, then a workspace query is assumed; the routine
! 129: * only calculates the optimal size of the WORK array, returns
! 130: * this value as the first entry of the WORK array, and no error
! 131: * message related to LWORK is issued by XERBLA.
! 132: *
! 133: * IWORK (workspace/output) INTEGER array, dimension (LIWORK)
! 134: * On exit, if INFO = 0, IWORK(1) returns the optimal LIWORK.
! 135: *
! 136: * LIWORK (input) INTEGER
! 137: * The dimension of the array IWORK. LIWORK >= max(1,10*N)
! 138: * if the eigenvectors are desired, and LIWORK >= max(1,8*N)
! 139: * if only the eigenvalues are to be computed.
! 140: * If LIWORK = -1, then a workspace query is assumed; the
! 141: * routine only calculates the optimal size of the IWORK array,
! 142: * returns this value as the first entry of the IWORK array, and
! 143: * no error message related to LIWORK is issued by XERBLA.
! 144: *
! 145: * INFO (output) INTEGER
! 146: * On exit, INFO
! 147: * = 0: successful exit
! 148: * < 0: if INFO = -i, the i-th argument had an illegal value
! 149: * > 0: if INFO = 1X, internal error in DLARRE,
! 150: * if INFO = 2X, internal error in ZLARRV.
! 151: * Here, the digit X = ABS( IINFO ) < 10, where IINFO is
! 152: * the nonzero error code returned by DLARRE or
! 153: * ZLARRV, respectively.
! 154: *
! 155: * Further Details
! 156: * ===============
! 157: *
! 158: * Based on contributions by
! 159: * Inderjit Dhillon, IBM Almaden, USA
! 160: * Osni Marques, LBNL/NERSC, USA
! 161: * Christof Voemel, LBNL/NERSC, USA
! 162: *
! 163: * =====================================================================
! 164: *
! 165: * .. Local Scalars ..
! 166: LOGICAL TRYRAC
! 167: * ..
! 168: * .. External Subroutines ..
! 169: EXTERNAL ZSTEMR
! 170: * ..
! 171: * .. Executable Statements ..
! 172: INFO = 0
! 173: TRYRAC = .FALSE.
! 174:
! 175: CALL ZSTEMR( JOBZ, RANGE, N, D, E, VL, VU, IL, IU,
! 176: $ M, W, Z, LDZ, N, ISUPPZ, TRYRAC, WORK, LWORK,
! 177: $ IWORK, LIWORK, INFO )
! 178: *
! 179: * End of ZSTEGR
! 180: *
! 181: END
CVSweb interface <joel.bertrand@systella.fr>
![[BACK]](/cvsweb/icons/back.gif){kind=icon}
Return to zstegr.f CVS log ![[TXT]](/cvsweb/icons/text.gif){kind=icon}
![[DIR]](/cvsweb/icons/dir.gif){kind=icon}
Up to [local] / rpl / lapack / lapack