SGTSV - solve the equation A*X = B,
SYNOPSIS
SUBROUTINE SGTSV( N, NRHS, DL, D, DU, B, LDB, INFO )
INTEGER INFO, LDB, N, NRHS
REAL B( LDB, * ), D( * ), DL( * ), DU( * )
PURPOSE
SGTSV solves the equation A*X = B, where A is an n by n
tridiagonal matrix, by Gaussian elimination with partial
pivoting.
Note that the equation A'*X = B may be solved by inter
changing the order of the arguments DU and DL.
ARGUMENTS
N (input) INTEGER
The order of the matrix A. N >= 0.
NRHS (input) INTEGER
The number of right hand sides, i.e., the number
of columns of the matrix B. NRHS >= 0.
DL (input/output) REAL array, dimension (N-1)
On entry, DL must contain the (n-1) sub-diagonal
elements of A.
On exit, DL 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
DL(1), ..., DL(n-2).
D (input/output) REAL array, dimension (N)
On entry, D must contain the diagonal elements of
A.
On exit, D is overwritten by the n diagonal ele
ments of U.
DU (input/output) REAL array, dimension (N-1)
On entry, DU must contain the (n-1) super-diagonal
elements of A.
On exit, DU is overwritten by the (n-1) elements
of the first super-diagonal of U.
B (input/output) REAL array, dimension (LDB,NRHS)
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.
The leading dimension of the array B. LDB >=
max(1,N).
INFO (output) INTEGER
= 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.
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