SUBROUTINE DLAGTF( N, A, LAMBDA, B, C, TOL, D, IN, INFO) INTEGER N, INFO INTEGER IN(*) DOUBLE PRECISION LAMBDA, TOL DOUBLE PRECISION A(*), B(*), C(*), D(*) SUBROUTINE DLAGTF_64( N, A, LAMBDA, B, C, TOL, D, IN, INFO) INTEGER*8 N, INFO INTEGER*8 IN(*) DOUBLE PRECISION LAMBDA, TOL DOUBLE PRECISION A(*), B(*), C(*), D(*)
SUBROUTINE LAGTF( [N], A, LAMBDA, B, C, TOL, D, IN, [INFO]) INTEGER :: N, INFO INTEGER, DIMENSION(:) :: IN REAL(8) :: LAMBDA, TOL REAL(8), DIMENSION(:) :: A, B, C, D SUBROUTINE LAGTF_64( [N], A, LAMBDA, B, C, TOL, D, IN, [INFO]) INTEGER(8) :: N, INFO INTEGER(8), DIMENSION(:) :: IN REAL(8) :: LAMBDA, TOL REAL(8), DIMENSION(:) :: A, B, C, D
void dlagtf(int n, double *a, double lambda, double *b, double *c, double tol, double *d, int *in, int *info);
void dlagtf_64(long n, double *a, double lambda, double *b, double *c, double tol, double *d, long *in, long *info);
The factorization is obtained by Gaussian elimination with partial pivoting and implicit row scaling.
The parameter LAMBDA is included in the routine so that SLAGTF may be used, in conjunction with SLAGTS, to obtain eigenvectors of T by inverse iteration.
On exit, A is overwritten by the n diagonal elements of the upper triangular matrix U of the factorization of T.
On exit, B is overwritten by the (n-1) super-diagonal elements of the matrix U of the factorization of T.
On exit, C is overwritten by the (n-1) sub-diagonal elements of the matrix L of the factorization of T.
abs( u(j,j) ).le. norm( (T - lambda*I)(j) )*TOL,
where norm( A(j) ) denotes the sum of the absolute values of the jth row of the matrix A. If no such j exists then IN(n) is returned as zero. If IN(n) is returned as positive, then a diagonal element of U is small, indicating that (T - lambda*I) is singular or nearly singular,