sptrfs - improve the computed solution to a system of linear equations when the coefficient matrix is symmetric positive definite and tridiagonal, and provides error bounds and backward error estimates for the solution
SUBROUTINE SPTRFS( N, NRHS, DIAG, OFFD, DIAGF, OFFDF, B, LDB, X, * LDX, FERR, BERR, WORK, INFO) INTEGER N, NRHS, LDB, LDX, INFO REAL DIAG(*), OFFD(*), DIAGF(*), OFFDF(*), B(LDB,*), X(LDX,*), FERR(*), BERR(*), WORK(*)
SUBROUTINE SPTRFS_64( N, NRHS, DIAG, OFFD, DIAGF, OFFDF, B, LDB, X, * LDX, FERR, BERR, WORK, INFO) INTEGER*8 N, NRHS, LDB, LDX, INFO REAL DIAG(*), OFFD(*), DIAGF(*), OFFDF(*), B(LDB,*), X(LDX,*), FERR(*), BERR(*), WORK(*)
SUBROUTINE PTRFS( [N], [NRHS], DIAG, OFFD, DIAGF, OFFDF, B, [LDB], * X, [LDX], FERR, BERR, [WORK], [INFO]) INTEGER :: N, NRHS, LDB, LDX, INFO REAL, DIMENSION(:) :: DIAG, OFFD, DIAGF, OFFDF, FERR, BERR, WORK REAL, DIMENSION(:,:) :: B, X
SUBROUTINE PTRFS_64( [N], [NRHS], DIAG, OFFD, DIAGF, OFFDF, B, [LDB], * X, [LDX], FERR, BERR, [WORK], [INFO]) INTEGER(8) :: N, NRHS, LDB, LDX, INFO REAL, DIMENSION(:) :: DIAG, OFFD, DIAGF, OFFDF, FERR, BERR, WORK REAL, DIMENSION(:,:) :: B, X
#include <sunperf.h>
void sptrfs(int n, int nrhs, float *diag, float *offd, float *diagf, float *offdf, float *b, int ldb, float *x, int ldx, float *ferr, float *berr, int *info);
void sptrfs_64(long n, long nrhs, float *diag, float *offd, float *diagf, float *offdf, float *b, long ldb, float *x, long ldx, float *ferr, float *berr, long *info);
sptrfs improves the computed solution to a system of linear equations when the coefficient matrix is symmetric positive definite and tridiagonal, and provides error bounds and backward error estimates for the solution.
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).
X(j)
(i.e., the smallest relative change in
any element of A or B that makes X(j)
an exact solution).
dimension(2*N)
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value