dtprfs

NAME

dtprfs - provide error bounds and backward error estimates for the solution to a system of linear equations with a triangular packed coefficient matrix

SYNOPSIS

  SUBROUTINE DTPRFS( UPLO, TRANSA, DIAG, N, NRHS, A, B, LDB, X, LDX, 
 *      FERR, BERR, WORK, WORK2, INFO)
  CHARACTER * 1 UPLO, TRANSA, DIAG
  INTEGER N, NRHS, LDB, LDX, INFO
  INTEGER WORK2(*)
  DOUBLE PRECISION A(*), B(LDB,*), X(LDX,*), FERR(*), BERR(*), WORK(*)
 
  SUBROUTINE DTPRFS_64( UPLO, TRANSA, DIAG, N, NRHS, A, B, LDB, X, 
 *      LDX, FERR, BERR, WORK, WORK2, INFO)
  CHARACTER * 1 UPLO, TRANSA, DIAG
  INTEGER*8 N, NRHS, LDB, LDX, INFO
  INTEGER*8 WORK2(*)
  DOUBLE PRECISION A(*), B(LDB,*), X(LDX,*), FERR(*), BERR(*), WORK(*)

F95 INTERFACE

  SUBROUTINE TPRFS( UPLO, [TRANSA], DIAG, N, NRHS, A, B, [LDB], X, 
 *       [LDX], FERR, BERR, [WORK], [WORK2], [INFO])
  CHARACTER(LEN=1) :: UPLO, TRANSA, DIAG
  INTEGER :: N, NRHS, LDB, LDX, INFO
  INTEGER, DIMENSION(:) :: WORK2
  REAL(8), DIMENSION(:) :: A, FERR, BERR, WORK
  REAL(8), DIMENSION(:,:) :: B, X
 
  SUBROUTINE TPRFS_64( UPLO, [TRANSA], DIAG, N, NRHS, A, B, [LDB], X, 
 *       [LDX], FERR, BERR, [WORK], [WORK2], [INFO])
  CHARACTER(LEN=1) :: UPLO, TRANSA, DIAG
  INTEGER(8) :: N, NRHS, LDB, LDX, INFO
  INTEGER(8), DIMENSION(:) :: WORK2
  REAL(8), DIMENSION(:) :: A, FERR, BERR, WORK
  REAL(8), DIMENSION(:,:) :: B, X

C INTERFACE

#include <sunperf.h>

void dtprfs(char uplo, char transa, char diag, int n, int nrhs, double *a, double *b, int ldb, double *x, int ldx, double *ferr, double *berr, int *info);

void dtprfs_64(char uplo, char transa, char diag, long n, long nrhs, double *a, double *b, long ldb, double *x, long ldx, double *ferr, double *berr, long *info);

PURPOSE

dtprfs provides error bounds and backward error estimates for the solution to a system of linear equations with a triangular packed coefficient matrix.

The solution matrix X must be computed by STPTRS or some other means before entering this routine. STPRFS does not do iterative refinement because doing so cannot improve the backward error.

ARGUMENTS

* UPLO (input)
* TRANSA (input): Specifies the form of the system of equations:
* DIAG (input)
* N (input): The order of the matrix A. N >= 0.
* NRHS (input): The number of right hand sides, i.e., the number of columns of the matrices B and X. NRHS >= 0.
* A (input): The upper or lower triangular matrix A, packed columnwise in a linear array. The j-th column of A is stored in the array A as follows: if UPLO = 'U', A(i + (j-1)*j/2) = A(i,j) for 1<=i<=j; if UPLO = 'L', A(i + (j-1)*(2*n-j)/2) = A(i,j) for j<=i<=n. If DIAG = 'U', the diagonal elements of A are not referenced and are assumed to be 1.
* B (input): The right hand side matrix B.
* LDB (input): The leading dimension of the array B. LDB >= max(1,N).
* X (input): The solution matrix X.
* LDX (input): The leading dimension of the array X. LDX >= max(1,N).
* FERR (output): The estimated forward error bound for each solution vector X(j) (the j-th column of the solution matrix X). If XTRUE is the true solution corresponding to X(j), FERR(j) is an estimated upper bound for the magnitude of the largest element in (X(j) - XTRUE) divided by the magnitude of the largest element in X(j). The estimate is as reliable as the estimate for RCOND, and is almost always a slight overestimate of the true error.
* BERR (output): The componentwise relative backward error of each solution vector X(j) (i.e., the smallest relative change in any element of A or B that makes X(j) an exact solution).
* WORK (workspace): dimension(3*N)
* WORK2 (workspace)
* INFO (output)