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sstevd (3)
  • >> sstevd (3) ( Solaris man: Библиотечные вызовы )
  • 
    NAME
         sstevd - compute all eigenvalues and, optionally,  eigenvec-
         tors of a real symmetric tridiagonal matrix
    
    SYNOPSIS
         SUBROUTINE SSTEVD( JOBZ, N,  D,  E,  Z,  LDZ,  WORK,  LWORK,
                   IWORK, LIWORK, INFO )
    
         CHARACTER JOBZ
    
         INTEGER INFO, LDZ, LIWORK, LWORK, N
    
         INTEGER IWORK( * )
    
         REAL D( * ), E( * ), WORK( * ), Z( LDZ, * )
    
    
    
         #include <sunperf.h>
    
         void sstevd(char jobz, int n, float *d, float *e, float *sz,
                   int ldz, int *info) ;
    
    PURPOSE
         SSTEVD computes all eigenvalues and,  optionally,  eigenvec-
         tors of a real symmetric tridiagonal matrix. If eigenvectors
         are desired, it uses a divide and conquer algorithm.
    
         The divide and conquer algorithm makes very mild assumptions
         about  floating  point  arithmetic. It will work on machines
         with a guard digit  in  add/subtract,  or  on  those  binary
         machines  without  guard digits which subtract like the Cray
         X-MP, Cray Y-MP, Cray C-90, or Cray-2. It could  conceivably
         fail  on  hexadecimal  or  decimal  machines  without  guard
         digits, but we know of none.
    
    
    ARGUMENTS
         JOBZ      (input) CHARACTER*1
                   = 'N':  Compute eigenvalues only;
                   = 'V':  Compute eigenvalues and eigenvectors.
    
         N         (input) INTEGER
                   The order of the matrix.  N >= 0.
    
         D         (input/output) REAL array, dimension (N)
                   On entry, the n diagonal elements of the tridiago-
                   nal  matrix  A.   On exit, if INFO = 0, the eigen-
                   values in ascending order.
    
         E         (input/output) REAL array, dimension (N)
                   On entry, the (n-1) subdiagonal  elements  of  the
                   tridiagonal  matrix A, stored in elements 1 to N-1
                   of E; E(N) need not be set, but  is  used  by  the
                   routine.   On  exit,  the  contents  of E are des-
                   troyed.
    
         Z         (output) REAL array, dimension (LDZ, N)
                   If JOBZ = 'V', then if INFO = 0,  Z  contains  the
                   orthonormal eigenvectors of the matrix A, with the
                   i-th column of Z holding the  eigenvector  associ-
                   ated  with  D(i).   If  JOBZ  = 'N', then Z is not
                   referenced.
    
         LDZ       (input) INTEGER
                   The leading dimension of the array Z.  LDZ  >=  1,
                   and if JOBZ = 'V', LDZ >= max(1,N).
    
         WORK      (workspace/output) REAL array,
                   dimension (LWORK) On exit, if LWORK >  0,  WORK(1)
                   returns the optimal LWORK.
    
         LWORK     (input) INTEGER
                   The dimension of the array WORK.  If JOBZ   =  'N'
                   or  N <= 1 then LWORK must be at least 1.  If JOBZ
                   = 'V' and N > 1 then LWORK must be at least ( 1  +
                   3*N  +  2*N*lg N + 2*N**2 ), where lg( N ) = smal-
                   lest integer k such that 2**k >= N.
    
         IWORK     (workspace/output)   INTEGER   array,    dimension
                   (LIWORK)
                   On exit, if  LIWORK  >  0,  IWORK(1)  returns  the
                   optimal LIWORK.
    
         LIWORK    (input) INTEGER
                   The dimension of the array IWORK.  If JOBZ  =  'N'
                   or N <= 1 then LIWORK must be at least 1.  If JOBZ
                   = 'V' and N > 1  then  LIWORK  must  be  at  least
                   2+5*N.
    
         INFO      (output) INTEGER
                   = 0:  successful exit
                   < 0:  if INFO = -i, the i-th argument had an ille-
                   gal value
                   > 0:  if INFO = i, the algorithm  failed  to  con-
                   verge;  i  off-diagonal elements of E did not con-
                   verge to zero.
    
    
    
    


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