NAG FL Interface
f07fff (dpoequ)

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: $\mathbf{a}(\mathbf{lda},*)$ – Real (Kind=nag_wp) array Input

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

On entry: the matrix $A$ whose scaling factors are to be computed. Only the diagonal elements of the array a are referenced.

3: $\mathbf{lda}$ – Integer Input

On entry: the first dimension of the array a as declared in the (sub)program from which f07fff is called.

Constraint: $\mathbf{lda}\ge \max (1,\mathbf{n})$.

4: $\mathbf{s}\left(\mathbf{n}\right)$ – Real (Kind=nag_wp) array Output

On exit: if $\mathbf{info}=\mathbf{0}$, s contains the diagonal elements of the scaling matrix $S$.

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

On exit: if $\mathbf{info}=\mathbf{0}$, scond contains the ratio of the smallest value of s to the largest value of s. If $\mathbf{scond}\ge 0.1$ and amax is neither too large nor too small, it is not worth scaling by $S$.

6: $\mathbf{amax}$ – Real (Kind=nag_wp) Output

On exit: $\max \left|a_{ij}\right|$. If amax is very close to overflow or underflow, the matrix $A$ should be scaled.

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.

$\mathbf{info}>0$

The $⟨\mathit{\text{value}}⟩$th diagonal element of $A$ is not positive (and hence $A$ cannot be positive definite).

7 Accuracy

8 Parallelism and Performance

9 Further Comments

10 Example

10.1 Program Text

10.2 Program Data

10.3 Program Results