dptcon(3P) Sun Performance Library dptcon(3P)NAMEdptcon - compute the reciprocal of the condition number (in the 1-norm)
of a real symmetric positive definite tridiagonal matrix using the fac‐
torization A = L*D*L**T or A = U**T*D*U computed by DPTTRF
SYNOPSIS
SUBROUTINE DPTCON(N, D, E, ANORM, RCOND, WORK, INFO)
INTEGER N, INFO
DOUBLE PRECISION ANORM, RCOND
DOUBLE PRECISION D(*), E(*), WORK(*)
SUBROUTINE DPTCON_64(N, D, E, ANORM, RCOND, WORK, INFO)
INTEGER*8 N, INFO
DOUBLE PRECISION ANORM, RCOND
DOUBLE PRECISION D(*), E(*), WORK(*)
F95 INTERFACE
SUBROUTINE PTCON([N], D, E, ANORM, RCOND, [WORK], [INFO])
INTEGER :: N, INFO
REAL(8) :: ANORM, RCOND
REAL(8), DIMENSION(:) :: D, E, WORK
SUBROUTINE PTCON_64([N], D, E, ANORM, RCOND, [WORK], [INFO])
INTEGER(8) :: N, INFO
REAL(8) :: ANORM, RCOND
REAL(8), DIMENSION(:) :: D, E, WORK
C INTERFACE
#include <sunperf.h>
void dptcon(int n, double *d, double *e, double anorm, double *rcond,
int *info);
void dptcon_64(long n, double *d, double *e, double anorm, double
*rcond, long *info);
PURPOSEdptcon computes the reciprocal of the condition number (in the 1-norm)
of a real symmetric positive definite tridiagonal matrix using the fac‐
torization A = L*D*L**T or A = U**T*D*U computed by DPTTRF.
Norm(inv(A)) is computed by a direct method, and the reciprocal of the
condition number is computed as
RCOND = 1 / (ANORM * norm(inv(A))).
ARGUMENTS
N (input) The order of the matrix A. N >= 0.
D (input) The n diagonal elements of the diagonal matrix D from the
factorization of A, as computed by DPTTRF.
E (input) The (n-1) off-diagonal elements of the unit bidiagonal factor
U or L from the factorization of A, as computed by DPTTRF.
ANORM (input)
The 1-norm of the original matrix A.
RCOND (output)
The reciprocal of the condition number of the matrix A, com‐
puted as RCOND = 1/(ANORM * AINVNM), where AINVNM is the
1-norm of inv(A) computed in this routine.
WORK (workspace)
dimension(N)
INFO (output)
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value
FURTHER DETAILS
The method used is described in Nicholas J. Higham, "Efficient Algo‐
rithms for Computing the Condition Number of a Tridiagonal Matrix",
SIAM J. Sci. Stat. Comput., Vol. 7, No. 1, January 1986.
6 Mar 2009 dptcon(3P)
