LAPACK  3.4.1
LAPACK: Linear Algebra PACKage
sptcon.f File Reference

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Functions/Subroutines

subroutine SPTCON (N, D, E, ANORM, RCOND, WORK, INFO)
 SPTCON

Function/Subroutine Documentation

subroutine SPTCON ( INTEGER  N,
REAL, dimension( * )  D,
REAL, dimension( * )  E,
REAL  ANORM,
REAL  RCOND,
REAL, dimension( * )  WORK,
INTEGER  INFO 
)

SPTCON

Download SPTCON + dependencies [TGZ] [ZIP] [TXT]
Purpose:

 SPTCON computes the reciprocal of the condition number (in the
 1-norm) of a real symmetric positive definite tridiagonal matrix
 using the factorization A = L*D*L**T or A = U**T*D*U computed by
 SPTTRF.

 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:
[in]N
          N is INTEGER
          The order of the matrix A.  N >= 0.
 
[in]D
          D is REAL array, dimension (N)
          The n diagonal elements of the diagonal matrix D from the
          factorization of A, as computed by SPTTRF.
 
[in]E
          E is REAL 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 SPTTRF.
 
[in]ANORM
          ANORM is REAL
          The 1-norm of the original matrix A.
 
[out]RCOND
          RCOND is REAL
          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.
 
[out]WORK
          WORK is REAL array, dimension (N)
 
[out]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:
November 2011
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 119 of file sptcon.f.

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