
dptrfs.f(3) LAPACK dptrfs.f(3)
NAME
dptrfs.f 
SYNOPSIS
Functions/Subroutines
subroutine dptrfs (N, NRHS, D, E, DF, EF, B, LDB, X, LDX, FERR, BERR, WORK, INFO)
DPTRFS
Function/Subroutine Documentation
subroutine dptrfs (integerN, integerNRHS, double precision, dimension( * )D, double precision,
dimension( * )E, double precision, dimension( * )DF, double precision, dimension( * )EF,
double precision, dimension( ldb, * )B, integerLDB, double precision, dimension( ldx, *
)X, integerLDX, double precision, dimension( * )FERR, double precision, dimension( *
)BERR, double precision, dimension( * )WORK, integerINFO)
DPTRFS
Purpose:
DPTRFS improves the computed solution to a system of linear
equations when the coefficient matrix is symmetric positive definite
and tridiagonal, and provides error bounds and backward error
estimates for the solution.
Parameters:
N
N is INTEGER
The order of the matrix A. N >= 0.
NRHS
NRHS is INTEGER
The number of right hand sides, i.e., the number of columns
of the matrix B. NRHS >= 0.
D
D is DOUBLE PRECISION array, dimension (N)
The n diagonal elements of the tridiagonal matrix A.
E
E is DOUBLE PRECISION array, dimension (N1)
The (n1) subdiagonal elements of the tridiagonal matrix A.
DF
DF is DOUBLE PRECISION array, dimension (N)
The n diagonal elements of the diagonal matrix D from the
factorization computed by DPTTRF.
EF
EF is DOUBLE PRECISION array, dimension (N1)
The (n1) subdiagonal elements of the unit bidiagonal factor
L from the factorization computed by DPTTRF.
B
B is DOUBLE PRECISION array, dimension (LDB,NRHS)
The right hand side matrix B.
LDB
LDB is INTEGER
The leading dimension of the array B. LDB >= max(1,N).
X
X is DOUBLE PRECISION array, dimension (LDX,NRHS)
On entry, the solution matrix X, as computed by DPTTRS.
On exit, the improved solution matrix X.
LDX
LDX is INTEGER
The leading dimension of the array X. LDX >= max(1,N).
FERR
FERR is DOUBLE PRECISION array, dimension (NRHS)
The forward error bound for each solution vector
X(j) (the jth 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
element in (X(j)  XTRUE) divided by the magnitude of the
largest element in X(j).
BERR
BERR is 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
WORK is DOUBLE PRECISION array, dimension (2*N)
INFO
INFO is INTEGER
= 0: successful exit
< 0: if INFO = i, the ith argument had an illegal value
Internal Parameters:
ITMAX is the maximum number of steps of iterative refinement.
Author:
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
September 2012
Definition at line 163 of file dptrfs.f.
Author
Generated automatically by Doxygen for LAPACK from the source code.
Version 3.4.2 Tue Sep 25 2012 dptrfs.f(3) 
