# zptcon.f man page

zptcon.f

## Synopsis

### Functions/Subroutines

subroutine **zptcon** (**N**, D, E, ANORM, RCOND, RWORK, INFO)**ZPTCON**

## Function/Subroutine Documentation

### subroutine zptcon (integer N, double precision, dimension( * ) D, complex*16, dimension( * ) E, double precision ANORM, double precision RCOND, double precision, dimension( * ) RWORK, integer INFO)

**ZPTCON**

**Purpose:**

ZPTCON computes the reciprocal of the condition number (in the 1-norm) of a complex Hermitian positive definite tridiagonal matrix using the factorization A = L*D*L**H or A = U**H*D*U computed by ZPTTRF. 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))).

**Parameters:**-
*N*N is INTEGER The order of the matrix A. N >= 0.

*D*D is DOUBLE PRECISION array, dimension (N) The n diagonal elements of the diagonal matrix D from the factorization of A, as computed by ZPTTRF.

*E*E is COMPLEX*16 array, dimension (N-1) The (n-1) off-diagonal elements of the unit bidiagonal factor U or L from the factorization of A, as computed by ZPTTRF.

*ANORM*ANORM is DOUBLE PRECISION The 1-norm of the original matrix A.

*RCOND*RCOND is DOUBLE PRECISION The reciprocal of the condition number of the matrix A, computed as RCOND = 1/(ANORM * AINVNM), where AINVNM is the 1-norm of inv(A) computed in this routine.

*RWORK*RWORK is DOUBLE PRECISION array, dimension (N)

*INFO*INFO is INTEGER = 0: successful exit < 0: if INFO = -i, the i-th argument had an illegal value

**Author:**-
Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date:**December 2016

**Further Details:**

The method used is described in Nicholas J. Higham, "Efficient Algorithms for Computing the Condition Number of a Tridiagonal Matrix", SIAM J. Sci. Stat. Comput., Vol. 7, No. 1, January 1986.

Definition at line 121 of file zptcon.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page zptcon(3) is an alias of zptcon.f(3).

Tue Nov 14 2017 Version 3.8.0 LAPACK