- SUBROUTINE ZTPCON(
- NORM, UPLO, DIAG, N, AP, RCOND, WORK, RWORK, INFO )
- CHARACTER DIAG, NORM, UPLO
- INTEGER INFO, N
- DOUBLE PRECISION RCOND
- DOUBLE PRECISION RWORK( * )
- COMPLEX*16 AP( * ), WORK( * )
PURPOSEZTPCON estimates the reciprocal of the condition number of a packed triangular matrix A, in either the 1-norm or the infinity-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)) ).
- 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*16 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) DOUBLE PRECISION
- The reciprocal of the condition number of the matrix A, computed as RCOND = 1/(norm(A) * norm(inv(A))).
- WORK (workspace) COMPLEX*16 array, dimension (2*N)
- RWORK (workspace) DOUBLE PRECISION array, dimension (N)
- INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value