Contents
sgtsv - solve the equation A*X = B,
SUBROUTINE SGTSV(N, NRHS, LOW, D, UP, B, LDB, INFO)
INTEGER N, NRHS, LDB, INFO
REAL LOW(*), D(*), UP(*), B(LDB,*)
SUBROUTINE SGTSV_64(N, NRHS, LOW, D, UP, B, LDB, INFO)
INTEGER*8 N, NRHS, LDB, INFO
REAL LOW(*), D(*), UP(*), B(LDB,*)
F95 INTERFACE
SUBROUTINE GTSV([N], [NRHS], LOW, D, UP, B, [LDB], [INFO])
INTEGER :: N, NRHS, LDB, INFO
REAL, DIMENSION(:) :: LOW, D, UP
REAL, DIMENSION(:,:) :: B
SUBROUTINE GTSV_64([N], [NRHS], LOW, D, UP, B, [LDB], [INFO])
INTEGER(8) :: N, NRHS, LDB, INFO
REAL, DIMENSION(:) :: LOW, D, UP
REAL, DIMENSION(:,:) :: B
C INTERFACE
#include <sunperf.h>
void sgtsv(int n, int nrhs, float *low, float *diag, float
*up, float *b, int ldb, int *info);
void sgtsv_64(long n, long nrhs, float *low, float *diag,
float *up, float *b, long ldb, long *info);
sgtsv solves the equation
where A is an n by n tridiagonal matrix, by Gaussian elimi-
nation with partial pivoting.
Note that the equation A'*X = B may be solved by inter-
changing the order of the arguments DU and DL.
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 matrix B. NRHS >= 0.
LOW (input/output)
On entry, LOW must contain the (n-1) sub-diagonal
elements of A.
On exit, LOW is overwritten by the (n-2) elements
of the second super-diagonal of the upper triangu-
lar matrix U from the LU factorization of A, in
LOW(1), ..., LOW(n-2).
D (input/output)
On entry, D must contain the diagonal elements of
A.
On exit, D is overwritten by the n diagonal ele-
ments of U.
UP (input/output)
On entry, UP must contain the (n-1) super-diagonal
elements of A.
On exit, UP is overwritten by the (n-1) elements
of the first super-diagonal of U.
B (input/output)
On entry, the N by NRHS matrix of right hand side
matrix B. On exit, if INFO = 0, the N by NRHS
solution matrix 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 ille-
gal value
> 0: if INFO = i, U(i,i) is exactly zero, and the
solution has not been computed. The factorization
has not been completed unless i = N.