The order of the matrix

T

(

n

≥

0)

.

The number of eigenvectors to be found

(0

≤

m

≤

n

)

.

Arrays:

d

, of size

n

. The

n

diagonal elements of the tridiagonal matrix

T

.

e

, of size

n

.

The

(

n

-1)

subdiagonal elements of the tridiagonal matrix

T

, in elements 1 to

n

-1

.

e

[

n

-1]

need not be set.

w

, of size

n

.

The first

m

elements of

w

contain the eigenvalues for which eigenvectors are to be computed. The eigenvalues should be grouped by split-off block and ordered from smallest to largest within the block. (The output array

w

from

?stebz

with

ORDER

=

'B'

is expected here).

The size of

w

must be at least

max(1,

n

)

.

Array of size

n

.

The submatrix indices associated with the corresponding eigenvalues in

w

;

iblock

[

i

]

= 1, if eigenvalue

w

[

i

]

belongs to the first submatrix from the top,

iblock

[

i

]

= 2, if eigenvalue

w

[

i

]

belongs to the second submatrix, etc. (The output array

iblock

from

?stebz

is expected here).

Array of size

n

.

The splitting points, at which

T

breaks up into submatrices. The first submatrix consists of rows/columns 1 to

isplit

[0]

, the second submatrix consists of rows/columns

isplit

[0]

+1 through

isplit

[1]

, etc. (The output array

isplit

from

?stebz

is expected here).

orfac

specifies which eigenvectors should be orthogonalized. Eigenvectors that correspond to eigenvalues which are within

orfac

*

||T||

of each other are to be orthogonalized.

The leading dimension of the output array

z

;

ldz

≥

max(1,

n

)

.

Workspace array of size 5

n

.

Workspace array of size

n

.

Array of size

ldz

*

m

.

The computed eigenvectors. The eigenvector associated with the eigenvalue

w

[

i

]

is stored in the

(

i

+1)

-th column of

the matrix

Z

represented by

z

,

i

=0, ...,

m

-1

. Any vector that fails to converge is set to its current iterate after

maxits

iterations.

Array of size

m

.

On normal exit, all elements of

ifail

are zero. If one or more eigenvectors fail to converge after

maxits

iterations, then their indices are stored in the array

ifail

.

info

= 0

, the exit is successful.

info

< 0

: if

info

=

-i

, the

i

-th had an illegal value.

info

> 0

: if

info

=

i

, then

i

eigenvectors failed to converge in

maxits

iterations. Their indices are stored in the array

ifail

.