Computes an LU factorization of a general tridiagonal matrix with no pivoting (local blocked algorithm).
call sdttrf(n, dl, d, du, info)
call ddttrf(n, dl, d, du, info)
call cdttrf(n, dl, d, du, info)
call zdttrf(n, dl, d, du, info)
The ?dttrf routine computes an LU factorization of a real or complex tridiagonal matrix A using elimination without partial pivoting.
The factorization has the form A = L*U, where L is a product of unit lower bidiagonal matrices and U is upper triangular with nonzeros only in the main diagonal and first superdiagonal.
INTEGER. The order of the matrix A(n ≥ 0).
REAL for sdttrf
DOUBLE PRECISION for ddttrf
COMPLEX for cdttrf
COMPLEX*16 for zdttrf.
Arrays containing elements of A.
The array dl of DIMENSION(n - 1) contains the sub-diagonal elements of A.
The array d of DIMENSION n contains the diagonal elements of A.
The array du of DIMENSION(n - 1) contains the super-diagonal elements of A.
Overwritten by the (n-1) multipliers that define the matrix L from the LU factorization of A.
Overwritten by the n diagonal elements of the upper triangular matrix U from the LU factorization of A.
Overwritten by the (n-1) elements of the first super-diagonal of U.
INTEGER.
= 0: successful exit
< 0: if info = - i, the i-th argument had an illegal value,
> 0: if info = i, u(i,i) is exactly 0. The factorization has been completed, but the factor U is exactly singular. Division by 0 will occur if you use the factor U for solving a system of linear equations.