# stbtrs (l) - Linux Manuals

## NAME

STBTRS - solves a triangular system of the form A * X = B or A**T * X = B,

## SYNOPSIS

SUBROUTINE STBTRS(
UPLO, TRANS, DIAG, N, KD, NRHS, AB, LDAB, B, LDB, INFO )

CHARACTER DIAG, TRANS, UPLO

INTEGER INFO, KD, LDAB, LDB, N, NRHS

REAL AB( LDAB, * ), B( LDB, * )

## PURPOSE

STBTRS solves a triangular system of the form where A is a triangular band matrix of order N, and B is an N-by NRHS matrix. A check is made to verify that A is nonsingular.

## ARGUMENTS

UPLO (input) CHARACTER*1
= aqUaq: A is upper triangular;
= aqLaq: A is lower triangular.
TRANS (input) CHARACTER*1

Specifies the form the system of equations:
= aqNaq: A * X = B (No transpose)
= aqTaq: A**T * X = B (Transpose)
= aqCaq: A**H * X = B (Conjugate transpose = Transpose)
DIAG (input) CHARACTER*1

= aqNaq: A is non-unit triangular;
= aqUaq: A is unit triangular.
N (input) INTEGER
The order of the matrix A. N >= 0.
KD (input) INTEGER
The number of superdiagonals or subdiagonals of the triangular band matrix A. KD >= 0.
NRHS (input) INTEGER
The number of right hand sides, i.e., the number of columns of the matrix B. NRHS >= 0.
AB (input) REAL array, dimension (LDAB,N)
The upper or lower triangular band matrix A, stored in the first kd+1 rows of AB. The j-th column of A is stored in the j-th column of the array AB as follows: if UPLO = aqUaq, AB(kd+1+i-j,j) = A(i,j) for max(1,j-kd)<=i<=j; if UPLO = aqLaq, AB(1+i-j,j) = A(i,j) for j<=i<=min(n,j+kd). If DIAG = aqUaq, the diagonal elements of A are not referenced and are assumed to be 1.
LDAB (input) INTEGER
The leading dimension of the array AB. LDAB >= KD+1.
B (input/output) REAL array, dimension (LDB,NRHS)
On entry, the right hand side matrix B. On exit, if INFO = 0, 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
> 0: if INFO = i, the i-th diagonal element of A is zero, indicating that the matrix is singular and the solutions X have not been computed.