sptrfs
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.
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* N (input)
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The order of the matrix A. N >= 0.
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* NRHS (input)
-
The number of right hand sides, i.e., the number of columns
of the matrix B. NRHS >= 0.
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* DIAG (input)
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The n diagonal elements of the tridiagonal matrix A.
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* OFFD (input)
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The (n-1) subdiagonal elements of the tridiagonal matrix A.
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* DIAGF (input)
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The n diagonal elements of the diagonal matrix DIAG from the
factorization computed by SPTTRF.
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* OFFDF (input)
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The (n-1) subdiagonal elements of the unit bidiagonal factor
L from the factorization computed by SPTTRF.
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* B (input)
-
The right hand side matrix B.
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* LDB (input)
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The leading dimension of the array B. LDB >= max(1,N).
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* X (input/output)
-
On entry, the solution matrix X, as computed by SPTTRS.
On exit, the improved solution matrix X.
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* LDX (input)
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The leading dimension of the array X. LDX >= max(1,N).
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* FERR (output)
-
The 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).
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* BERR (output)
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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).
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* WORK (workspace)
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dimension(N)
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* INFO (output)
-