slagts.f(3)							      LAPACK							       slagts.f(3)

NAME

       slagts.f -

SYNOPSIS

   Functions/Subroutines
       subroutine slagts (JOB, N, A, B, C, D, IN, Y, TOL, INFO)
	   SLAGTS

Function/Subroutine Documentation
   subroutine slagts (integerJOB, integerN, real, dimension( * )A, real, dimension( * )B, real, dimension( * )C, real, dimension( * )D, integer,
       dimension( * )IN, real, dimension( * )Y, realTOL, integerINFO)
       SLAGTS

       Purpose:

	    SLAGTS may be used to solve one of the systems of equations

	       (T - lambda*I)*x = y   or   (T - lambda*I)**T*x = y,

	    where T is an n by n tridiagonal matrix, for x, following the
	    factorization of (T - lambda*I) as

	       (T - lambda*I) = P*L*U ,

	    by routine SLAGTF. The choice of equation to be solved is
	    controlled by the argument JOB, and in each case there is an option
	    to perturb zero or very small diagonal elements of U, this option
	    being intended for use in applications such as inverse iteration.

       Parameters:
	   JOB

		     JOB is INTEGER
		     Specifies the job to be performed by SLAGTS as follows:
		     =	1: The equations  (T - lambda*I)x = y  are to be solved,
			   but diagonal elements of U are not to be perturbed.
		     = -1: The equations  (T - lambda*I)x = y  are to be solved
			   and, if overflow would otherwise occur, the diagonal
			   elements of U are to be perturbed. See argument TOL
			   below.
		     =	2: The equations  (T - lambda*I)**Tx = y  are to be solved,
			   but diagonal elements of U are not to be perturbed.
		     = -2: The equations  (T - lambda*I)**Tx = y  are to be solved
			   and, if overflow would otherwise occur, the diagonal
			   elements of U are to be perturbed. See argument TOL
			   below.

	   N

		     N is INTEGER
		     The order of the matrix T.

	   A

		     A is REAL array, dimension (N)
		     On entry, A must contain the diagonal elements of U as
		     returned from SLAGTF.

	   B

		     B is REAL array, dimension (N-1)
		     On entry, B must contain the first super-diagonal elements of
		     U as returned from SLAGTF.

	   C

		     C is REAL array, dimension (N-1)
		     On entry, C must contain the sub-diagonal elements of L as
		     returned from SLAGTF.

	   D

		     D is REAL array, dimension (N-2)
		     On entry, D must contain the second super-diagonal elements
		     of U as returned from SLAGTF.

	   IN

		     IN is INTEGER array, dimension (N)
		     On entry, IN must contain details of the matrix P as returned
		     from SLAGTF.

	   Y

		     Y is REAL array, dimension (N)
		     On entry, the right hand side vector y.
		     On exit, Y is overwritten by the solution vector x.

	   TOL

		     TOL is REAL
		     On entry, with  JOB .lt. 0, TOL should be the minimum
		     perturbation to be made to very small diagonal elements of U.
		     TOL should normally be chosen as about eps*norm(U), where eps
		     is the relative machine precision, but if TOL is supplied as
		     non-positive, then it is reset to eps*max( abs( u(i,j) ) ).
		     If  JOB .gt. 0  then TOL is not referenced.

		     On exit, TOL is changed as described above, only if TOL is
		     non-positive on entry. Otherwise TOL is unchanged.

	   INFO

		     INFO is INTEGER
		     = 0   : successful exit
		     .lt. 0: if INFO = -i, the i-th argument had an illegal value
		     .gt. 0: overflow would occur when computing the INFO(th)
			     element of the solution vector x. This can only occur
			     when JOB is supplied as positive and either means
			     that a diagonal element of U is very small, or that
			     the elements of the right-hand side vector y are very
			     large.

       Author:
	   Univ. of Tennessee

	   Univ. of California Berkeley

	   Univ. of Colorado Denver

	   NAG Ltd.

       Date:
	   November 2011

       Definition at line 162 of file slagts.f.

Author
       Generated automatically by Doxygen for LAPACK from the source code.

Version 3.4.1							  Sun May 26 2013						       slagts.f(3)