SPPCON - estimate the reciprocal of the condition number
(in the 1-norm) of a real symmetric positive definite
packed matrix using the Cholesky factorization A = U**T*U
or A = L*L**T computed by SPPTRF
SYNOPSIS
SUBROUTINE SPPCON( UPLO, N, AP, ANORM, RCOND, WORK, IWORK,
INFO )
CHARACTER UPLO
INTEGER INFO, N
REAL ANORM, RCOND
INTEGER IWORK( * )
REAL AP( * ), WORK( * )
PURPOSE
SPPCON estimates the reciprocal of the condition number
(in the 1-norm) of a real symmetric positive definite
packed matrix using the Cholesky factorization A = U**T*U
or A = L*L**T computed by SPPTRF. An estimate is obtained
for norm(inv(A)), and the reciprocal of the condition num
ber is computed as RCOND = 1 / (ANORM * norm(inv(A))).
ARGUMENTS
UPLO (input) CHARACTER*1
= 'U': Upper triangle of A is stored;
= 'L': Lower triangle of A is stored.
N (input) INTEGER
The order of the matrix A. N >= 0.
AP (input) REAL array, dimension (N*(N+1)/2)
The triangular factor U or L from the Cholesky
factorization A = U**T*U or A = L*L**T, packed
columnwise in a linear array. The j-th column of
U or L is stored in the array AP as follows: if
UPLO = 'U', AP(i + (j-1)*j/2) = U(i,j) for
1<=i<=j; if UPLO = 'L', AP(i + (j-1)*(2n-j)/2) =
L(i,j) for j<=i<=n.
ANORM (input) REAL
The 1-norm (or infinity-norm) of the symmetric
matrix A.
RCOND (output) REAL
The reciprocal of the condition number of the
matrix A, computed as RCOND = 1/(ANORM * AINVNM),
where AINVNM is an estimate of the 1-norm of
WORK (workspace) REAL array, dimension (3*N)
IWORK (workspace) INTEGER array, dimension (N)
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an ille
gal value
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