sgtsv (l)  Linux Manuals
sgtsv: solves the equation A*X = B,
NAME
SGTSV  solves 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 where A is an n by n tridiagonal matrix, by Gaussian elimination with partial pivoting.Note that the equation Aaq*X = B may be solved by interchanging 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 (N1)
 On entry, DL must contain the (n1) subdiagonal elements of A. On exit, DL is overwritten by the (n2) elements of the second superdiagonal of the upper triangular matrix U from the LU factorization of A, in DL(1), ..., DL(n2).
 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 elements of U.
 DU (input/output) REAL array, dimension (N1)
 On entry, DU must contain the (n1) superdiagonal elements of A. On exit, DU is overwritten by the (n1) elements of the first superdiagonal 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.
 LDB (input) INTEGER
 The leading dimension of the array B. LDB >= max(1,N).
 INFO (output) INTEGER

= 0: successful exit
< 0: if INFO = i, the ith argument had an illegal 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.