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dgerfs (3)
  • >> dgerfs (3) ( Solaris man: Библиотечные вызовы )
  • 
    NAME
         dgerfs - improve the computed solution to a system of linear
         equations and provides error bounds and backward error esti-
         mates for the solution
    
    SYNOPSIS
         SUBROUTINE DGERFS( TRANS, N, NRHS, A, LDA, AF,  LDAF,  IPIV,
                   B, LDB, X, LDX, FERR, BERR, WORK, IWORK, INFO )
    
         CHARACTER TRANS
    
         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 dgerfs(char trans, 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
         DGERFS improves the computed solution to a system of  linear
         equations and provides error bounds and backward error esti-
         mates for the solution.
    
    
    ARGUMENTS
         TRANS     (input) CHARACTER*1
                   Specifies the form of the system of equations:
                   = 'N':  A * X = B     (No transpose)
                   = 'T':  A**T * X = B  (Transpose)
                   = 'C':  A**H * X = B  (Conjugate transpose = Tran-
                   spose)
    
         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 original N-by-N matrix A.
    
         LDA       (input) INTEGER
                   The leading dimension of  the  array  A.   LDA  >=
                   max(1,N).
    
         AF        (input) DOUBLE PRECISION array, dimension (LDAF,N)
                   The factors L and U from  the  factorization  A  =
                   P*L*U as computed by DGETRF.
    
         LDAF      (input) INTEGER
                   The leading dimension of the array  AF.   LDAF  >=
                   max(1,N).
    
         IPIV      (input) INTEGER array, dimension (N)
                   The pivot indices from DGETRF; for 1<=i<=N, row  i
                   of the matrix was interchanged with row IPIV(i).
    
         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
                   DGETRS.  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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