• NAME
• SYNOPSIS
• F95 INTERFACE
• C INTERFACE
• PURPOSE
• ARGUMENTS

NAME

dgttrs - solve one of the systems of equations A*X = B or A'*X = B,

SYNOPSIS

  SUBROUTINE DGTTRS( TRANSA, N, NRHS, LOW, DIAG, UP1, UP2, IPIVOT, B, 
 *      LDB, INFO)
  CHARACTER * 1 TRANSA
  INTEGER N, NRHS, LDB, INFO
  INTEGER IPIVOT(*)
  DOUBLE PRECISION LOW(*), DIAG(*), UP1(*), UP2(*), B(LDB,*)

  SUBROUTINE DGTTRS_64( TRANSA, N, NRHS, LOW, DIAG, UP1, UP2, IPIVOT, 
 *      B, LDB, INFO)
  CHARACTER * 1 TRANSA
  INTEGER*8 N, NRHS, LDB, INFO
  INTEGER*8 IPIVOT(*)
  DOUBLE PRECISION LOW(*), DIAG(*), UP1(*), UP2(*), B(LDB,*)

F95 INTERFACE

  SUBROUTINE GTTRS( [TRANSA], [N], [NRHS], LOW, DIAG, UP1, UP2, 
 *       IPIVOT, B, [LDB], [INFO])
  CHARACTER(LEN=1) :: TRANSA
  INTEGER :: N, NRHS, LDB, INFO
  INTEGER, DIMENSION(:) :: IPIVOT
  REAL(8), DIMENSION(:) :: LOW, DIAG, UP1, UP2
  REAL(8), DIMENSION(:,:) :: B

  SUBROUTINE GTTRS_64( [TRANSA], [N], [NRHS], LOW, DIAG, UP1, UP2, 
 *       IPIVOT, B, [LDB], [INFO])
  CHARACTER(LEN=1) :: TRANSA
  INTEGER(8) :: N, NRHS, LDB, INFO
  INTEGER(8), DIMENSION(:) :: IPIVOT
  REAL(8), DIMENSION(:) :: LOW, DIAG, UP1, UP2
  REAL(8), DIMENSION(:,:) :: B

C INTERFACE

#include <sunperf.h>

void dgttrs(char transa, int n, int nrhs, double *low, double *diag, double *up1, double *up2, int *ipivot, double *b, int ldb, int *info);

void dgttrs_64(char transa, long n, long nrhs, double *low, double *diag, double *up1, double *up2, long *ipivot, double *b, long ldb, long *info);

PURPOSE

dgttrs solves one of the systems of equations A*X = B or A'*X = B, with a tridiagonal matrix A using the LU factorization computed by SGTTRF.

ARGUMENTS

• TRANSA (input)
  Specifies the form of the system of equations. = 'N': A * X = B (No transpose)

   = 'T':  A'* X  = B  (Transpose)

   = 'C':  A'* X  = B  (Conjugate transpose  = Transpose)

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

• NRHS (input)
  The number of right hand sides, i.e., the number of columns of the matrix B. NRHS > = 0.

• LOW (input)
  The (n-1) multipliers that define the matrix L from the LU factorization of A.

• 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 super-diagonal of U.

• UP2 (input)
  The (n-2) elements of the second super-diagonal 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.

• B (input/output)
  On entry, the matrix of right hand side vectors B. On exit, B is overwritten by the solution vectors X.

• LDB (input)
  The leading dimension of the array B. LDB > = max(1,N).

• INFO (output)
  

   = 0:  successful exit

   < 0:  if INFO  = -i, the i-th argument had an illegal value