NAG FL Interface
c02ajf (quadratic_​real)

1 Purpose

2 Specification

3 Description

4 References

5 Arguments

1: $\mathbf{a}$ – Real (Kind=nag_wp) Input

On entry: must contain $a$, the coefficient of $z^2$.

2: $\mathbf{b}$ – Real (Kind=nag_wp) Input

On entry: must contain $b$, the coefficient of $z$.

3: $\mathbf{c}$ – Real (Kind=nag_wp) Input

On entry: must contain $c$, the constant coefficient.

4: $\mathbf{zsm}\left(2\right)$ – Real (Kind=nag_wp) array Output

On exit: the real and imaginary parts of the smallest root in magnitude are stored in $\mathbf{zsm}\left(1\right)$ and $\mathbf{zsm}\left(2\right)$ respectively.

5: $\mathbf{zlg}\left(2\right)$ – Real (Kind=nag_wp) array Output

On exit: the real and imaginary parts of the largest root in magnitude are stored in $\mathbf{zlg}\left(1\right)$ and $\mathbf{zlg}\left(2\right)$ respectively.

6: $\mathbf{ifail}$ – Integer Input/Output

On entry: ifail must be set to $0$, $\mathrm{-1}$ or $1$ to set behaviour on detection of an error; these values have no effect when no error is detected.

A value of $0$ causes the printing of an error message and program execution will be halted; otherwise program execution continues. A value of $\mathrm{-1}$ means that an error message is printed while a value of $1$ means that it is not.

If halting is not appropriate, the value $\mathrm{-1}$ or $1$ is recommended. If message printing is undesirable, then the value $1$ is recommended. Otherwise, the value $0$ is recommended. When the value $-\mathbf{1}$ or $\mathbf{1}$ is used it is essential to test the value of ifail on exit.

On exit: $\mathbf{ifail}=\mathbf{0}$ unless the routine detects an error or a warning has been flagged (see Section 6).

6 Error Indicators and Warnings

$\mathbf{ifail}=1$

On entry, $\mathbf{a}=0.0$.

$\mathbf{ifail}=2$

On entry, $\mathbf{a}=0.0$ and $\mathbf{b}=0.0$.

$\mathbf{ifail}=3$

On entry, $\mathbf{a}=0.0$ and the root $-\mathbf{c}/\mathbf{b}$ overflows: $\mathbf{a}=⟨\mathit{\text{value}}⟩$, $\mathbf{c}=⟨\mathit{\text{value}}⟩$ and $\mathbf{b}=⟨\mathit{\text{value}}⟩$.

$\mathbf{ifail}=4$

On entry, $\mathbf{c}=0.0$ and the root $-\mathbf{b}/\mathbf{a}$ overflows: $\mathbf{c}=⟨\mathit{\text{value}}⟩$, $\mathbf{b}=⟨\mathit{\text{value}}⟩$ and $\mathbf{a}=⟨\mathit{\text{value}}⟩$.

$\mathbf{ifail}=5$

On entry, b is so large that ${\mathbf{b}}^2$ is indistinguishable from $({\mathbf{b}}^2-4\times \mathbf{a}\times \mathbf{c})$ and the root $-\mathbf{b}/\mathbf{a}$ overflows: $\mathbf{b}=⟨\mathit{\text{value}}⟩$, $\mathbf{a}=⟨\mathit{\text{value}}⟩$ and $\mathbf{c}=⟨\mathit{\text{value}}⟩$.

$\mathbf{ifail}=-99$

An unexpected error has been triggered by this routine. Please contact NAG.

See Section 7 in the Introduction to the NAG Library FL Interface for further information.

$\mathbf{ifail}=-399$

Your licence key may have expired or may not have been installed correctly.

See Section 8 in the Introduction to the NAG Library FL Interface for further information.

$\mathbf{ifail}=-999$

Dynamic memory allocation failed.

See Section 9 in the Introduction to the NAG Library FL Interface for further information.

7 Accuracy

8 Parallelism and Performance

9 Further Comments

10 Example

10.1 Program Text

10.2 Program Data

10.3 Program Results