sgtcon

NAME

sgtcon - estimate the reciprocal of the condition number of a real tridiagonal matrix A using the LU factorization as computed by SGTTRF

SYNOPSIS

  SUBROUTINE SGTCON( NORM, N, LOW, DIAG, UP1, UP2, IPIVOT, ANORM, 
 *      RCOND, WORK, IWORK2, INFO)
  CHARACTER * 1 NORM
  INTEGER N, INFO
  INTEGER IPIVOT(*), IWORK2(*)
  REAL ANORM, RCOND
  REAL LOW(*), DIAG(*), UP1(*), UP2(*), WORK(*)
 
  SUBROUTINE SGTCON_64( NORM, N, LOW, DIAG, UP1, UP2, IPIVOT, ANORM, 
 *      RCOND, WORK, IWORK2, INFO)
  CHARACTER * 1 NORM
  INTEGER*8 N, INFO
  INTEGER*8 IPIVOT(*), IWORK2(*)
  REAL ANORM, RCOND
  REAL LOW(*), DIAG(*), UP1(*), UP2(*), WORK(*)

F95 INTERFACE

  SUBROUTINE GTCON( NORM, [N], LOW, DIAG, UP1, UP2, IPIVOT, ANORM, 
 *       RCOND, [WORK], [IWORK2], [INFO])
  CHARACTER(LEN=1) :: NORM
  INTEGER :: N, INFO
  INTEGER, DIMENSION(:) :: IPIVOT, IWORK2
  REAL :: ANORM, RCOND
  REAL, DIMENSION(:) :: LOW, DIAG, UP1, UP2, WORK
 
  SUBROUTINE GTCON_64( NORM, [N], LOW, DIAG, UP1, UP2, IPIVOT, ANORM, 
 *       RCOND, [WORK], [IWORK2], [INFO])
  CHARACTER(LEN=1) :: NORM
  INTEGER(8) :: N, INFO
  INTEGER(8), DIMENSION(:) :: IPIVOT, IWORK2
  REAL :: ANORM, RCOND
  REAL, DIMENSION(:) :: LOW, DIAG, UP1, UP2, WORK

C INTERFACE

#include <sunperf.h>

void sgtcon(char norm, int n, float *low, float *diag, float *up1, float *up2, int *ipivot, float anorm, float *rcond, int *info);

void sgtcon_64(char norm, long n, float *low, float *diag, float *up1, float *up2, long *ipivot, float anorm, float *rcond, long *info);

PURPOSE

sgtcon estimates the reciprocal of the condition number of a real tridiagonal matrix A using the LU factorization as computed by SGTTRF.

An estimate is obtained for norm(inv(A)), and the reciprocal of the condition number is computed as RCOND = 1 / (ANORM * norm(inv(A))).

ARGUMENTS

* NORM (input): Specifies whether the 1-norm condition number or the infinity-norm condition number is required:
* N (input): The order of the matrix A. N >= 0.
* LOW (input): The (n-1) multipliers that define the matrix L from the LU factorization of A as computed by SGTTRF.
* DIAG (input): The n diagonal elements of the upper triangular matrix U from the LU factorization of A.
* UP1 (input): The (n-1) elements of the first superdiagonal of U.
* UP2 (input): The (n-2) elements of the second superdiagonal of U.
* IPIVOT (input): The pivot indices; for 1 <= i <= n, row i of the matrix was interchanged with row IPIVOT(i). IPIVOT(i) will always be either i or i+1; IPIVOT(i) = i indicates a row interchange was not required.
* ANORM (input): If NORM = '1' or 'O', the 1-norm of the original matrix A. If NORM = 'I', the infinity-norm of the original matrix A.
* RCOND (output): 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 inv(A) computed in this routine.
* WORK (workspace): dimension(2*N)
* IWORK2 (workspace)
* INFO (output)