NAG FL Interface
f07jgf (dptcon)

1 Purpose

2 Specification

3 Description

4 References

5 Arguments

1: $\mathbf{n}$ – Integer Input

On entry: $n$, the order of the matrix $A$.

Constraint: $\mathbf{n}\ge 0$.

2: $\mathbf{d}\left(*\right)$ – Real (Kind=nag_wp) array Input

Note: the dimension of the array d must be at least $\max (1,\mathbf{n})$.

On entry: must contain the $n$ diagonal elements of the diagonal matrix $D$ from the $LD{L}^{\mathrm{T}}$ factorization of $A$.

3: $\mathbf{e}\left(*\right)$ – Real (Kind=nag_wp) array Input

Note: the dimension of the array e must be at least $\max (1,\mathbf{n}-1)$.

On entry: must contain the $(n-1)$ subdiagonal elements of the unit lower bidiagonal matrix $L$. (e can also be regarded as the superdiagonal of the unit upper bidiagonal matrix $U$ from the $U^{\mathrm{T}}DU$ factorization of $A$.)

4: $\mathbf{anorm}$ – Real (Kind=nag_wp) Input

On entry: the $1$-norm of the original matrix $A$, which may be computed by calling f06rpf with its argument $\mathbf{norm}=\text{'1'}$. anorm must be computed either before calling f07jdf or else from a copy of the original matrix $A$.

Constraint: $\mathbf{anorm}\ge 0.0$.

5: $\mathbf{rcond}$ – Real (Kind=nag_wp) Output

On exit: the reciprocal condition number, $1/{\kappa }_1\left(A\right)=1/\left({\Vert A\Vert }_1{\Vert A^{-1}\Vert }_1\right)$.

6: $\mathbf{work}\left(\mathbf{n}\right)$ – Real (Kind=nag_wp) array Workspace

7: $\mathbf{info}$ – Integer Output

On exit: $\mathbf{info}=0$ unless the routine detects an error (see Section 6).

6 Error Indicators and Warnings

$\mathbf{info}<0$

If $\mathbf{info}=-i$, argument $i$ had an illegal value. An explanatory message is output, and execution of the program is terminated.

7 Accuracy

8 Parallelism and Performance

9 Further Comments

10 Example

10.1 Program Text

10.2 Program Data

10.3 Program Results