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LAPACK
3.7.0
LAPACK: Linear Algebra PACKage
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subroutine sptrfs | ( | integer | N, |
integer | NRHS, | ||
real, dimension( * ) | D, | ||
real, dimension( * ) | E, | ||
real, dimension( * ) | DF, | ||
real, dimension( * ) | EF, | ||
real, dimension( ldb, * ) | B, | ||
integer | LDB, | ||
real, dimension( ldx, * ) | X, | ||
integer | LDX, | ||
real, dimension( * ) | FERR, | ||
real, dimension( * ) | BERR, | ||
real, dimension( * ) | WORK, | ||
integer | INFO | ||
) |
SPTRFS
Download SPTRFS + dependencies [TGZ] [ZIP] [TXT]
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.
[in] | N | N is INTEGER The order of the matrix A. N >= 0. |
[in] | NRHS | NRHS is INTEGER The number of right hand sides, i.e., the number of columns of the matrix B. NRHS >= 0. |
[in] | D | D is REAL array, dimension (N) The n diagonal elements of the tridiagonal matrix A. |
[in] | E | E is REAL array, dimension (N-1) The (n-1) subdiagonal elements of the tridiagonal matrix A. |
[in] | DF | DF is REAL array, dimension (N) The n diagonal elements of the diagonal matrix D from the factorization computed by SPTTRF. |
[in] | EF | EF is REAL array, dimension (N-1) The (n-1) subdiagonal elements of the unit bidiagonal factor L from the factorization computed by SPTTRF. |
[in] | B | B is REAL array, dimension (LDB,NRHS) The right hand side matrix B. |
[in] | LDB | LDB is INTEGER The leading dimension of the array B. LDB >= max(1,N). |
[in,out] | X | X is REAL array, dimension (LDX,NRHS) On entry, the solution matrix X, as computed by SPTTRS. On exit, the improved solution matrix X. |
[in] | LDX | LDX is INTEGER The leading dimension of the array X. LDX >= max(1,N). |
[out] | FERR | FERR is REAL array, dimension (NRHS) 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). |
[out] | BERR | BERR is REAL array, dimension (NRHS) 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). |
[out] | WORK | WORK is REAL array, dimension (2*N) |
[out] | INFO | INFO is INTEGER = 0: successful exit < 0: if INFO = -i, the i-th argument had an illegal value |
ITMAX is the maximum number of steps of iterative refinement.
Definition at line 165 of file sptrfs.f.