Provided by: liblapack-doc_3.3.1-1_all

**NAME**

LAPACK-3 - solves one of the systems of equations A*X = B or A**T*X = B,

**SYNOPSIS**

SUBROUTINE DGTTS2( ITRANS, N, NRHS, DL, D, DU, DU2, IPIV, B, LDB ) INTEGER ITRANS, LDB, N, NRHS INTEGER IPIV( * ) DOUBLE PRECISION B( LDB, * ), D( * ), DL( * ), DU( * ), DU2( * )

**PURPOSE**

DGTTS2 solves one of the systems of equations A*X = B or A**T*X = B, with a tridiagonal matrix A using the LU factorization computed by DGTTRF.

**ARGUMENTS**

ITRANS (input) INTEGER Specifies the form of the system of equations. = 0: A * X = B (No transpose) = 1: A**T* X = B (Transpose) = 2: A**T* X = B (Conjugate transpose = Transpose) N (input) INTEGER The order of the matrix A. NRHS (input) INTEGER The number of right hand sides, i.e., the number of columns of the matrix B. NRHS >= 0. DL (input) DOUBLE PRECISION array, dimension (N-1) The (n-1) multipliers that define the matrix L from the LU factorization of A. D (input) DOUBLE PRECISION array, dimension (N) The n diagonal elements of the upper triangular matrix U from the LU factorization of A. DU (input) DOUBLE PRECISION array, dimension (N-1) The (n-1) elements of the first super-diagonal of U. DU2 (input) DOUBLE PRECISION array, dimension (N-2) The (n-2) elements of the second super-diagonal of U. IPIV (input) INTEGER array, dimension (N) The pivot indices; for 1 <= i <= n, row i of the matrix was interchanged with row IPIV(i). IPIV(i) will always be either i or i+1; IPIV(i) = i indicates a row interchange was not required. B (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS) On entry, the matrix of right hand side vectors B. On exit, B is overwritten by the solution vectors X. LDB (input) INTEGER The leading dimension of the array B. LDB >= max(1,N). LAPACK auxiliary routine (version 3.2) April 2011 DGTTS2(3lapack)