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sgttrf (3)
  • >> sgttrf (3) ( Solaris man: Библиотечные вызовы )
  • 
    NAME
         sgttrf - compute an LU factorization of a  real  tridiagonal
         matrix  A  using  elimination  with partial pivoting and row
         interchanges
    
    SYNOPSIS
         SUBROUTINE SGTTRF( N, DL, D, DU, DU2, IPIV, INFO )
    
         INTEGER INFO, N
    
         INTEGER IPIV( * )
    
         REAL D( * ), DL( * ), DU( * ), DU2( * )
    
    
    
         #include <sunperf.h>
    
         void sgttrf(int n, float *dl, float  *d,  float  *du,  float
                   *du2, int *ipivot, int *info) ;
    
    PURPOSE
         SGTTRF computes an LU factorization of  a  real  tridiagonal
         matrix  A  using  elimination  with partial pivoting and row
         interchanges.
    
         The factorization has the form
            A = L * U
         where L is a product of permutation and unit lower  bidiago-
         nal matrices and U is upper triangular with nonzeros in only
         the main diagonal and first two superdiagonals.
    
    
    ARGUMENTS
         N         (input) INTEGER
                   The order of the matrix A.  N >= 0.
    
         DL        (input/output) REAL array, dimension (N-1)
                   On entry, DL must contain  the  (n-1)  subdiagonal
                   elements  of A.  On exit, DL is overwritten by the
                   (n-1) multipliers that define the  matrix  L  from
                   the LU factorization of A.
    
         D         (input/output) REAL array, dimension (N)
                   On entry, D must contain the diagonal elements  of
                   A.   On  exit,  D is overwritten by the n diagonal
                   elements of the upper triangular matrix U from the
                   LU factorization of A.
    
         DU        (input/output) REAL array, dimension (N-1)
                   On entry, DU must contain the (n-1)  superdiagonal
                   elements  of A.  On exit, DU is overwritten by the
                   (n-1) elements of the first superdiagonal of U.
    
         DU2       (output) REAL array, dimension (N-2)
                   On exit, DU2 is overwritten by the (n-2)  elements
                   of the second superdiagonal of U.
    
         IPIV      (output) INTEGER array, dimension (N)
                   The pivot indices; for 1 <= i <= n, row i  of  the
                   matrix was interchanged with row IPIV(i).  IPIV(i)
                   will always be either i or i+1; IPIV(i) = i  indi-
                   cates a row interchange was not required.
    
         INFO      (output) INTEGER
                   = 0:  successful exit
                   < 0:  if INFO = -i, the i-th argument had an ille-
                   gal value
                   > 0:  if INFO = i, U(i,i)  is  exactly  zero.  The
                   factorization has been completed, but the factor U
                   is exactly singular, and  division  by  zero  will
                   occur  if  it  is  used to solve a system of equa-
                   tions.
    
    
    
    


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