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# sgttrs

```
NAME
SGTTRS - solve 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
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 superdiagonal of U.

DU2     (input) REAL array, dimension (N-2)
The (n-2) elements of the second superdiagonal 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 indi-
cates a row interchange was not required.

B       (input/output) REAL array, dimension (LDB,NRHS)
On entry, the right hand side matrix B.  On exit, B
is overwritten by the 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 i-th argument had an illegal
value
```