solves a triangular system of the form A * X = B or A**T * X = B,
- SUBROUTINE DTBTRS(
UPLO, TRANS, DIAG, N, KD, NRHS, AB, LDAB, B,
LDB, INFO )
DIAG, TRANS, UPLO
INFO, KD, LDAB, LDB, N, NRHS
PRECISION AB( LDAB, * ), B( LDB, * )
DTBTRS 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.
- UPLO (input) CHARACTER*1
= 'U': A is upper triangular;
= 'L': A is lower triangular.
- TRANS (input) CHARACTER*1
Specifies the form the system of equations:
= 'N': A * X = B (No transpose)
= 'T': A**T * X = B (Transpose)
= 'C': A**H * X = B (Conjugate transpose = Transpose)
- DIAG (input) CHARACTER*1
= 'N': A is non-unit triangular;
= 'U': 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) DOUBLE PRECISION 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 = 'U', AB(kd+1+i-j,j) = A(i,j) for max(1,j-kd)<=i<=j;
if UPLO = 'L', AB(1+i-j,j) = A(i,j) for j<=i<=min(n,j+kd).
If DIAG = 'U', 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) DOUBLE PRECISION 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.