lagtf Interface

public interface lagtf

LAGTF factorizes the matrix (T - lambdaI), where T is an n by n tridiagonal matrix and lambda is a scalar, as T - lambdaI = PLU, where P is a permutation matrix, L is a unit lower tridiagonal matrix with at most one non-zero sub-diagonal elements per column and U is an upper triangular matrix with at most two non-zero super-diagonal elements per column. The factorization is obtained by Gaussian elimination with partial pivoting and implicit row scaling. The parameter LAMBDA is included in the routine so that LAGTF may be used, in conjunction with DLAGTS, to obtain eigenvectors of T by inverse iteration.


Subroutines

public pure subroutine dlagtf(n, a, lambda, b, c, tol, d, in, info)

Arguments

Type IntentOptional Attributes Name
integer(kind=ilp), intent(in) :: n
real(kind=dp), intent(inout) :: a(*)
real(kind=dp), intent(in) :: lambda
real(kind=dp), intent(inout) :: b(*)
real(kind=dp), intent(inout) :: c(*)
real(kind=dp), intent(in) :: tol
real(kind=dp), intent(out) :: d(*)
integer(kind=ilp), intent(out) :: in(*)
integer(kind=ilp), intent(out) :: info

public pure subroutine slagtf(n, a, lambda, b, c, tol, d, in, info)

Arguments

Type IntentOptional Attributes Name
integer(kind=ilp), intent(in) :: n
real(kind=sp), intent(inout) :: a(*)
real(kind=sp), intent(in) :: lambda
real(kind=sp), intent(inout) :: b(*)
real(kind=sp), intent(inout) :: c(*)
real(kind=sp), intent(in) :: tol
real(kind=sp), intent(out) :: d(*)
integer(kind=ilp), intent(out) :: in(*)
integer(kind=ilp), intent(out) :: info

Module Procedures

public interface stdlib_dlagtf()

Arguments

None

public interface stdlib_slagtf()

Arguments

None