.TH SGTSV 1 "November 2006" " LAPACK routine (version 3.1) " " LAPACK routine (version 3.1) " .SH NAME SGTSV - the equation A*X = B, .SH SYNOPSIS .TP 18 SUBROUTINE SGTSV( N, NRHS, DL, D, DU, B, LDB, INFO ) .TP 18 .ti +4 INTEGER INFO, LDB, N, NRHS .TP 18 .ti +4 REAL B( LDB, * ), D( * ), DL( * ), DU( * ) .SH PURPOSE SGTSV solves the equation where A is an n by n tridiagonal matrix, by Gaussian elimination with partial pivoting. .br Note that the equation A\(aq*X = B may be solved by interchanging the order of the arguments DU and DL. .br .SH ARGUMENTS .TP 8 N (input) INTEGER The order of the matrix A. N >= 0. .TP 8 NRHS (input) INTEGER The number of right hand sides, i.e., the number of columns of the matrix B. NRHS >= 0. .TP 8 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 triangular matrix U from the LU factorization of A, in DL(1), ..., DL(n-2). .TP 8 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. .TP 8 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. .TP 8 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. .TP 8 LDB (input) INTEGER The leading dimension of the array B. LDB >= max(1,N). .TP 8 INFO (output) INTEGER = 0: successful exit .br < 0: if INFO = -i, the i-th argument had an illegal value .br > 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.