.TH "SRC/slagts.f" 3 "Version 3.12.0" "LAPACK" \" -*- nroff -*-
.ad l
.nh
.SH NAME
SRC/slagts.f
.SH SYNOPSIS
.br
.PP
.SS "Functions/Subroutines"

.in +1c
.ti -1c
.RI "subroutine \fBslagts\fP (job, n, a, b, c, d, in, y, tol, info)"
.br
.RI "\fBSLAGTS\fP solves the system of equations (T-λI)x = y or (T-λI)^Tx = y, where T is a general tridiagonal matrix and λ a scalar, using the LU factorization computed by slagtf\&. "
.in -1c
.SH "Function/Subroutine Documentation"
.PP 
.SS "subroutine slagts (integer job, integer n, real, dimension( * ) a, real, dimension( * ) b, real, dimension( * ) c, real, dimension( * ) d, integer, dimension( * ) in, real, dimension( * ) y, real tol, integer info)"

.PP
\fBSLAGTS\fP solves the system of equations (T-λI)x = y or (T-λI)^Tx = y, where T is a general tridiagonal matrix and λ a scalar, using the LU factorization computed by slagtf\&.  
.PP
\fBPurpose:\fP
.RS 4

.PP
.nf
!>
!> 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\&.
!> 
.fi
.PP
 
.RE
.PP
\fBParameters\fP
.RS 4
\fIJOB\fP 
.PP
.nf
!>          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\&.
!> 
.fi
.PP
.br
\fIN\fP 
.PP
.nf
!>          N is INTEGER
!>          The order of the matrix T\&.
!> 
.fi
.PP
.br
\fIA\fP 
.PP
.nf
!>          A is REAL array, dimension (N)
!>          On entry, A must contain the diagonal elements of U as
!>          returned from SLAGTF\&.
!> 
.fi
.PP
.br
\fIB\fP 
.PP
.nf
!>          B is REAL array, dimension (N-1)
!>          On entry, B must contain the first super-diagonal elements of
!>          U as returned from SLAGTF\&.
!> 
.fi
.PP
.br
\fIC\fP 
.PP
.nf
!>          C is REAL array, dimension (N-1)
!>          On entry, C must contain the sub-diagonal elements of L as
!>          returned from SLAGTF\&.
!> 
.fi
.PP
.br
\fID\fP 
.PP
.nf
!>          D is REAL array, dimension (N-2)
!>          On entry, D must contain the second super-diagonal elements
!>          of U as returned from SLAGTF\&.
!> 
.fi
.PP
.br
\fIIN\fP 
.PP
.nf
!>          IN is INTEGER array, dimension (N)
!>          On entry, IN must contain details of the matrix P as returned
!>          from SLAGTF\&.
!> 
.fi
.PP
.br
\fIY\fP 
.PP
.nf
!>          Y is REAL array, dimension (N)
!>          On entry, the right hand side vector y\&.
!>          On exit, Y is overwritten by the solution vector x\&.
!> 
.fi
.PP
.br
\fITOL\fP 
.PP
.nf
!>          TOL is REAL
!>          On entry, with  JOB < 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 > 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\&.
!> 
.fi
.PP
.br
\fIINFO\fP 
.PP
.nf
!>          INFO is INTEGER
!>          = 0: successful exit
!>          < 0: if INFO = -i, the i-th argument had an illegal value
!>          > 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\&.
!> 
.fi
.PP
 
.RE
.PP
\fBAuthor\fP
.RS 4
Univ\&. of Tennessee 

.PP
Univ\&. of California Berkeley 

.PP
Univ\&. of Colorado Denver 

.PP
NAG Ltd\&. 
.RE
.PP

.PP
Definition at line \fB162\fP of file \fBslagts\&.f\fP\&.
.SH "Author"
.PP 
Generated automatically by Doxygen for LAPACK from the source code\&.