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man pages->IRIX man pages -> complib/IMTQLV (3)
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Contents

```
_IMTQLV(3F)							   _IMTQLV(3F)

```

NAME[Toc][Back]

```     IMTQLV, SIMTQLV  -	 EISPACK routine.  This	subroutine is a	variant	of
IMTQL1.

```

SYNOPSYS[Toc][Back]

```	  subroutine  imtqlv(n,	d, e, e2, w, ind, ierr,	rv1)
integer	   n, ierr, ind(n)
double precision d(n), e(n), e2(n), w(n), rv1(n)

subroutine simtqlv(n,	d, e, e2, w, ind, ierr,	rv1)
integer	   n, ierr, ind(n)
real		   d(n), e(n), e2(n), w(n), rv1(n)

```

DESCRIPTION[Toc][Back]

```     This subroutine finds the eigenvalues of a	SYMMETRIC TRIDIAGONAL matrix
by	the implicit QL	method and associates with them	their corresponding
submatrix indices.

On	INPUT

N is the order of the matrix.

D contains	the diagonal elements of the input matrix.

E contains	the subdiagonal	elements of the	input matrix in	its last N-1
positions.	 E(1) is arbitrary.

E2	contains the squares of	the corresponding elements of E. E2(1) is
arbitrary.	 On OUTPUT

D and E are unaltered. Elements of	E2, corresponding to elements of E
regarded as negligible, have been replaced	by zero	causing	the matrix to
split into	a direct sum of	submatrices.  E2(1) is also set	to zero.

W contains	the eigenvalues	in ascending order.  If	an error exit is made,
the eigenvalues are correct and ordered for indices 1,2,...IERR-1,	but
may not be	the smallest eigenvalues.

IND contains the submatrix	indices	associated with	the corresponding
eigenvalues in W -- 1 for eigenvalues belonging to	the first submatrix
from the top, 2 for those belonging to the	second submatrix, etc.

IERR is set to ZERO       for normal return, J	     if	the J-th
eigenvalue	has not	been
determined after 30 iterations.

RV1 is a temporary	storage	array. Calls PYTHAG(A,B) for sqrt(A**2 +
B**2).  Questions and comments should be directed to B. S.	Garbow,
APPLIED MATHEMATICS DIVISION, ARGONNE NATIONAL LABORATORY

PPPPaaaaggggeeee 1111```
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