NAG FL Interface
e02zaf (dim2_​spline_​sort)

1 Purpose

2 Specification

3 Description

A set of $m$ data points with rectangular Cartesian coordinates $x_r,y_r$ are sorted into panels defined by lines parallel to the $y$ and $x$ axes. The intercepts of these lines on the $x$ and $y$ axes are given in $\mathbf{lamda}\left(\mathit{i}\right)$, for $\mathit{i}=5,6,\dots ,\mathbf{px}-4$ and $\mathbf{mu}\left(\mathit{j}\right)$, for $\mathit{j}=5,6,\dots ,\mathbf{py}-4$, respectively. The subroutine orders the data so that all points in a panel occur before data in succeeding panels, where the panels are numbered from bottom to top and then left to right, with the usual arrangement of axes, as shown in the diagram. Within a panel the points maintain their original order.

Figure 1

4 References

5 Arguments

1: $\mathbf{px}$ – Integer Input

2: $\mathbf{py}$ – Integer Input

On entry: px and py must specify eight more than the number of intercepts on the $x$ axis and $y$ axis, respectively.

Constraint: $\mathbf{px}\ge 8$ and $\mathbf{py}\ge 8$.

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

On entry: $\mathbf{lamda}\left(5\right)$ to $\mathbf{lamda}\left(\mathbf{px}-4\right)$ must contain, in nondecreasing order, the intercepts on the $x$ axis of the sides of the panels parallel to the $y$ axis.

4: $\mathbf{mu}\left(\mathbf{py}\right)$ – Real (Kind=nag_wp) array Input

On entry: $\mathbf{mu}\left(5\right)$ to $\mathbf{mu}\left(\mathbf{py}-4\right)$ must contain, in nondecreasing order, the intercepts on the $y$ axis of the sides of the panels parallel to the $x$ axis.

5: $\mathbf{m}$ – Integer Input

On entry: the number $m$ of data points.

6: $\mathbf{x}\left(\mathbf{m}\right)$ – Real (Kind=nag_wp) array Input

7: $\mathbf{y}\left(\mathbf{m}\right)$ – Real (Kind=nag_wp) array Input

On entry: the coordinates of the $\mathit{r}$th data point $(x_{\mathit{r}},y_{\mathit{r}})$, for $\mathit{r}=1,2,\dots ,m$.

8: $\mathbf{point}\left(\mathbf{npoint}\right)$ – Integer array Output

On exit: for $i=1,2,\dots ,\mathbf{npoint}$, $\mathbf{point}\left(m+i\right)=\mathrm{I1}$ is the index of the first point in panel $i$, $\mathbf{point}\left(\mathrm{I1}\right)=\mathrm{I2}$ is the index of the second point in panel $i$ and so on.

$\mathbf{point}\left(\mathrm{In}\right)=0$ indicates that $\mathbf{x}\left(\mathrm{In}\right),\mathbf{y}\left(\mathrm{In}\right)$ was the last point in the panel.

The coordinates of points in panel $i$ can be accessed in turn by means of the following instructions:

in = m + i
10 in = point(in)
If (in.eq. 0) Goto 20
xi = x(in)
yi = y(in)
.
.
.
Goto 10
20 ...

9: $\mathbf{npoint}$ – Integer Input

On entry: the dimension of the array point as declared in the (sub)program from which e02zaf is called.

Constraint: $\mathbf{npoint}\ge \mathbf{m}+(\mathbf{px}-7)\times (\mathbf{py}-7)$.

10: $\mathbf{adres}\left(\mathbf{nadres}\right)$ – Integer array Workspace

11: $\mathbf{nadres}$ – Integer Input

On entry: the value $(\mathbf{px}-7)\times (\mathbf{py}-7)$, the number of panels into which the $(x,y)$ plane is divided.

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

On entry: ifail must be set to $0$, $-1$ 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 $-1$ means that an error message is printed while a value of $1$ means that it is not.

If halting is not appropriate, the value $-1$ 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, $\mathit{I}=⟨\mathit{\text{value}}⟩$, $\mathbf{lamda}\left(\mathit{I}\right)=⟨\mathit{\text{value}}⟩$ and $\mathbf{lamda}\left(\mathit{I}-1\right)=⟨\mathit{\text{value}}⟩$.
Constraint: $\mathbf{lamda}\left(\mathit{I}\right)\ge \mathbf{lamda}\left(\mathit{I}-1\right)$.

On entry, $\mathit{I}=⟨\mathit{\text{value}}⟩$, $\mathbf{mu}\left(\mathit{I}\right)=⟨\mathit{\text{value}}⟩$ and $\mathbf{mu}\left(\mathit{I}-1\right)=⟨\mathit{\text{value}}⟩$.
Constraint: $\mathbf{mu}\left(\mathit{I}\right)\ge \mathbf{mu}\left(\mathit{I}-1\right)$.

$\mathbf{ifail}=2$

On entry, $\mathbf{m}=⟨\mathit{\text{value}}⟩$.
Constraint: $\mathbf{m}>0$.

On entry, $\mathbf{nadres}=⟨\mathit{\text{value}}⟩$, $\mathbf{px}=⟨\mathit{\text{value}}⟩$ and $\mathbf{py}=⟨\mathit{\text{value}}⟩$.
Constraint: $\mathbf{nadres}=(\mathbf{px}-7)\times (\mathbf{py}-7)$.

On entry, $\mathbf{npoint}=⟨\mathit{\text{value}}⟩$, $\mathbf{m}=⟨\mathit{\text{value}}⟩$, $\mathbf{px}=⟨\mathit{\text{value}}⟩$ and $\mathbf{py}=⟨\mathit{\text{value}}⟩$.
Constraint: $\mathbf{npoint}\ge \mathbf{m}+(\mathbf{px}-7)\times (\mathbf{py}-7)$.

On entry, $\mathbf{px}=⟨\mathit{\text{value}}⟩$.
Constraint: $\mathbf{px}\ge 8$.

On entry, $\mathbf{py}=⟨\mathit{\text{value}}⟩$.
Constraint: $\mathbf{py}\ge 8$.

$\mathbf{ifail}=-99$

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