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dsyrfs (3)
  • >> dsyrfs (3) ( Solaris man: Библиотечные вызовы )
  • 
    NAME
         dsyrfs - improve the computed solution to a system of linear
         equations  when the coefficient matrix is symmetric indefin-
         ite, and provides error bounds and backward error  estimates
         for the solution
    
    SYNOPSIS
         SUBROUTINE DSYRFS( UPLO, N, NRHS, A, LDA, AF, LDAF, IPIV, B,
                   LDB, X, LDX, FERR, BERR, WORK, IWORK, INFO )
    
         CHARACTER UPLO
    
         INTEGER INFO, LDA, LDAF, LDB, LDX, N, NRHS
    
         INTEGER IPIV( * ), IWORK( * )
    
         DOUBLE PRECISION A( LDA, * ), AF( LDAF, * ), B(  LDB,  *  ),
                   BERR( * ), FERR( * ), WORK( * ), X( LDX, * )
    
    
    
         #include <sunperf.h>
    
         void dsyrfs(char uplo, int n, int nrhs, double *da, int lda,
                   double *af, int ldaf, int *ipivot, double *db, int
                   ldb, double *dx, int  ldx,  double  *ferr,  double
                   *berr, int *info) ;
    
    PURPOSE
         DSYRFS improves the computed solution to a system of  linear
         equations  when the coefficient matrix is symmetric indefin-
         ite, and provides error bounds and backward error  estimates
         for the solution.
    
    
    ARGUMENTS
         UPLO      (input) CHARACTER*1
                   = 'U':  Upper triangle of A is stored;
                   = 'L':  Lower triangle of A is stored.
    
         N         (input) INTEGER
                   The order of the matrix A.  N >= 0.
    
         NRHS      (input) INTEGER
                   The number of right hand sides, i.e.,  the  number
                   of columns of the matrices B and X.  NRHS >= 0.
    
         A         (input) DOUBLE PRECISION array, dimension (LDA,N)
                   The symmetric matrix A.  If UPLO = 'U', the  lead-
                   ing N-by-N upper triangular part of A contains the
                   upper triangular part of the  matrix  A,  and  the
                   strictly   lower  triangular  part  of  A  is  not
                   referenced.  If UPLO =  'L',  the  leading  N-by-N
                   lower triangular part of A contains the lower tri-
                   angular part of the matrix  A,  and  the  strictly
                   upper triangular part of A is not referenced.
    
         LDA       (input) INTEGER
                   The leading dimension of  the  array  A.   LDA  >=
                   max(1,N).
    
         AF        (input) DOUBLE PRECISION array, dimension (LDAF,N)
                   The factored form of the matrix  A.   AF  contains
                   the  block  diagonal  matrix D and the multipliers
                   used to obtain the factor U or L from the factori-
                   zation A = U*D*U**T or A = L*D*L**T as computed by
                   DSYTRF.
    
         LDAF      (input) INTEGER
                   The leading dimension of the array  AF.   LDAF  >=
                   max(1,N).
    
         IPIV      (input) INTEGER array, dimension (N)
                   Details of the interchanges and the  block  struc-
                   ture of D as determined by DSYTRF.
    
         B         (input)   DOUBLE   PRECISION   array,    dimension
                   (LDB,NRHS)
                   The right hand side matrix B.
    
         LDB       (input) INTEGER
                   The leading dimension of  the  array  B.   LDB  >=
                   max(1,N).
    
         X         (input/output) DOUBLE PRECISION  array,  dimension
                   (LDX,NRHS)
                   On entry, the solution matrix X,  as  computed  by
                   DSYTRS.  On exit, the improved solution matrix X.
    
         LDX       (input) INTEGER
                   The leading dimension of  the  array  X.   LDX  >=
                   max(1,N).
    
         FERR      (output) DOUBLE PRECISION array, dimension (NRHS)
                   The estimated forward error bound for  each  solu-
                   tion  vector X(j) (the j-th column of the solution
                   matrix  X).   If  XTRUE  is  the   true   solution
                   corresponding  to  X(j),  FERR(j)  is an estimated
                   upper bound for the magnitude of the largest  ele-
                   ment in (X(j) - XTRUE) divided by the magnitude of
                   the largest element in X(j).  The estimate  is  as
                   reliable  as the estimate for RCOND, and is almost
                   always a slight overestimate of the true error.
    
         BERR      (output) DOUBLE PRECISION array, dimension (NRHS)
                   The componentwise relative backward error of  each
                   solution  vector X(j) (i.e., the smallest relative
                   change in any element of A or B that makes X(j) an
                   exact solution).
    
         WORK      (workspace)  DOUBLE  PRECISION  array,   dimension
                   (3*N)
    
         IWORK     (workspace) INTEGER array, dimension (N)
    
         INFO      (output) INTEGER
                   = 0:  successful exit
                   < 0:  if INFO = -i, the i-th argument had an ille-
                   gal value
    
    
    
    


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