ctpcon(3)

NAME

CTPCON - estimate the reciprocal of the condition number

of a packed triangular matrix A, in either the 1-norm or the in

finity-norm

SYNOPSIS

SUBROUTINE CTPCON( NORM, UPLO, DIAG, N, AP,  RCOND,  WORK,
RWORK, INFO )
    CHARACTER      DIAG, NORM, UPLO
    INTEGER        INFO, N
    REAL           RCOND
    REAL           RWORK( * )
    COMPLEX        AP( * ), WORK( * )

PURPOSE

CTPCON estimates the reciprocal of the condition number of

a packed triangular matrix A, in either the 1-norm or the infini

ty-norm. The norm of A is computed and an estimate is obtained

for norm(inv(A)), then the reciprocal of the condition number is

computed as

RCOND = 1 / ( norm(A) * norm(inv(A)) ).

ARGUMENTS

NORM (input) CHARACTER*1

Specifies whether the 1-norm condition number or

the infinity-norm condition number is required:
= '1' or 'O': 1-norm;
= 'I': Infinity-norm.

UPLO (input) CHARACTER*1

= 'U': A is upper triangular;
= 'L': A is lower triangular.

DIAG (input) CHARACTER*1

= 'N': A is non-unit triangular;
= 'U': A is unit triangular.

N (input) INTEGER

The order of the matrix A. N >= 0.

AP (input) COMPLEX array, dimension (N*(N+1)/2)

The upper or lower triangular matrix A, packed

columnwise in a linear array. The j-th column of A is stored in

the array AP as follows: if UPLO = 'U', AP(i + (j-1)*j/2) =

A(i,j) for 1<=i<=j; if UPLO = 'L', AP(i + (j-1)*(2n-j)/2) =

A(i,j) for j<=i<=n. If DIAG = 'U', the diagonal elements of A

are not referenced and are assumed to be 1.

RCOND (output) REAL

The reciprocal of the condition number of the ma

trix A, computed as RCOND = 1/(norm(A) * norm(inv(A))).

WORK (workspace) COMPLEX array, dimension (2*N)

RWORK (workspace) REAL array, dimension (N)

INFO (output) INTEGER

= 0: successful exit
< 0: if INFO = -i, the i-th argument had an ille

gal value

LAPACK version 3.0 15 June 2000

CTPCON(3)