NAME¶

SGTTRS - solves one of the systems of equations A*X = B or A'*X = B,

SYNOPSIS¶

SUBROUTINE SGTTRS(

TRANS, N, NRHS, DL, D, DU, DU2, IPIV, B, LDB, INFO )

CHARACTER TRANS INTEGER INFO, LDB, N, NRHS INTEGER IPIV( * ) REAL B( LDB, * ), D( * ), DL( * ), DU( * ), DU2( * )

PURPOSE¶

SGTTRS solves one of the systems of equations
A*X = B or A'*X = B, with a tridiagonal matrix A using the LU factorization computed by SGTTRF.

ARGUMENTS¶

TRANS (input) CHARACTER*1

Specifies the form of the system of equations. = 'N': A * X = B (No transpose)
= 'T': A'* X = B (Transpose)
= 'C': A'* 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) REAL array, dimension (N-1)

The (n-1) multipliers that define the matrix L from the LU factorization of A.

D (input) REAL array, dimension (N)

The n diagonal elements of the upper triangular matrix U from the LU factorization of A.

DU (input) REAL array, dimension (N-1)

The (n-1) elements of the first super-diagonal of U.

DU2 (input) REAL 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) REAL 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).

INFO (output) INTEGER

= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value