dgttrf (3p)

Name

dgttrf - compute an LU factorization of a real tridiagonal matrix A using elimination with partial pivoting and row interchanges

Synopsis

SUBROUTINE DGTTRF(N, LOW, D, UP1, UP2, IPIVOT, INFO)

INTEGER N, INFO
INTEGER IPIVOT(*)
DOUBLE PRECISION LOW(*), D(*), UP1(*), UP2(*)

SUBROUTINE DGTTRF_64(N, LOW, D, UP1, UP2, IPIVOT, INFO)

INTEGER*8 N, INFO
INTEGER*8 IPIVOT(*)
DOUBLE PRECISION LOW(*), D(*), UP1(*), UP2(*)




F95 INTERFACE
SUBROUTINE GTTRF(N, LOW, D, UP1, UP2, IPIVOT, INFO)

INTEGER :: N, INFO
INTEGER, DIMENSION(:) :: IPIVOT
REAL(8), DIMENSION(:) :: LOW, D, UP1, UP2

SUBROUTINE GTTRF_64(N, LOW, D, UP1, UP2, IPIVOT, INFO)

INTEGER(8) :: N, INFO
INTEGER(8), DIMENSION(:) :: IPIVOT
REAL(8), DIMENSION(:) :: LOW, D, UP1, UP2




C INTERFACE
#include <sunperf.h>

void dgttrf(int n, double *low, double *d, double  *up1,  double  *up2,
int *ipivot, int *info);

void  dgttrf_64(long  n,  double  *low,  double *d, double *up1, double
*up2, long *ipivot, long *info);

Description

Oracle Solaris Studio Performance Library                           dgttrf(3P)



NAME
       dgttrf  -  compute  an  LU factorization of a real tridiagonal matrix A
       using elimination with partial pivoting and row interchanges


SYNOPSIS
       SUBROUTINE DGTTRF(N, LOW, D, UP1, UP2, IPIVOT, INFO)

       INTEGER N, INFO
       INTEGER IPIVOT(*)
       DOUBLE PRECISION LOW(*), D(*), UP1(*), UP2(*)

       SUBROUTINE DGTTRF_64(N, LOW, D, UP1, UP2, IPIVOT, INFO)

       INTEGER*8 N, INFO
       INTEGER*8 IPIVOT(*)
       DOUBLE PRECISION LOW(*), D(*), UP1(*), UP2(*)




   F95 INTERFACE
       SUBROUTINE GTTRF(N, LOW, D, UP1, UP2, IPIVOT, INFO)

       INTEGER :: N, INFO
       INTEGER, DIMENSION(:) :: IPIVOT
       REAL(8), DIMENSION(:) :: LOW, D, UP1, UP2

       SUBROUTINE GTTRF_64(N, LOW, D, UP1, UP2, IPIVOT, INFO)

       INTEGER(8) :: N, INFO
       INTEGER(8), DIMENSION(:) :: IPIVOT
       REAL(8), DIMENSION(:) :: LOW, D, UP1, UP2




   C INTERFACE
       #include <sunperf.h>

       void dgttrf(int n, double *low, double *d, double  *up1,  double  *up2,
                 int *ipivot, int *info);

       void  dgttrf_64(long  n,  double  *low,  double *d, double *up1, double
                 *up2, long *ipivot, long *info);



PURPOSE
       dgttrf computes an LU factorization of  a  real  tridiagonal  matrix  A
       using elimination with partial pivoting and row interchanges.

       The factorization has the form
          A = L * U
       where  L is a product of permutation and unit lower bidiagonal matrices
       and U is upper triangular with nonzeros in only the main  diagonal  and
       first two superdiagonals.


ARGUMENTS
       N (input) The order of the matrix A.


       LOW (input/output)
                 On entry, LOW must contain the (n-1) sub-diagonal elements of
                 A.

                 On exit, LOW is overwritten by  the  (n-1)  multipliers  that
                 define the matrix L from the LU factorization of A.


       D (input/output)
                 On entry, D must contain the diagonal elements of A.

                 On  exit,  D is overwritten by the n diagonal elements of the
                 upper triangular matrix U from the LU factorization of A.


       UP1 (input/output)
                 On entry, UP1 must contain the (n-1) super-diagonal  elements
                 of A.

                 On  exit,  UP1  is  overwritten  by the (n-1) elements of the
                 first super-diagonal of U.


       UP2 (output)
                 On exit, UP2 is overwritten by the (n-2) elements of the sec-
                 ond super-diagonal of U.


       IPIVOT (output)
                 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.


       INFO (output)
                 = 0:  successful exit
                 < 0:  if INFO = -k, the k-th argument had an illegal value
                 > 0:  if INFO = k, U(k,k) is exactly zero. The  factorization
                 has been completed, but the factor U is exactly singular, and
                 division by zero will occur if it is used to solve  a  system
                 of equations.




                                  7 Nov 2015                        dgttrf(3P)