NAG Library Routine Document

g01agf  (withdraw_plot_scatter_2var)

 Contents

    1  Purpose
    7  Accuracy

1
Purpose

g01agf performs a scatter plot of two variables on a character printing device, with a chosen number of character positions in each direction.

2
Specification

Fortran Interface
Subroutine g01agf ( x, y, nobs, isort, nstepx, nstepy, ifail)
Integer, Intent (In):: nobs, nstepx, nstepy
Integer, Intent (Inout):: ifail
Integer, Intent (Out):: isort(nobs)
Real (Kind=nag_wp), Intent (In):: x(nobs)
Real (Kind=nag_wp), Intent (Inout):: y(nobs)
C Header Interface
#include nagmk26.h
void  g01agf_ ( const double x[], double y[], const Integer *nobs, Integer isort[], const Integer *nstepx, const Integer *nstepy, Integer *ifail)

3
Description

g01agf finds the range of the data in each dimension and calculates a step size for each division on the axes; these step sizes are selected from the list
0.1,0.15,0.2,0.25,0.4,0.5,0.6,0.75,0.8 × power of ​ 10 .  
The axes are drawn and annotated and data points are plotted on the nearest character position. The character plotted is either a digit 1 to 9 for the equivalent number of occurrences of a point at a particular character position, an alphabetic A–Z for 1035 occurrences, or * if there are more than 35 coincident occurrences. Axes are drawn on all sides of the plot with the left-hand and bottom ones annotated; zero axes are also marked if included in the plotting area.
The Fortran logical unit number used for the output is the current advisory message unit number defined for each implementation. This number may be changed by an appropriate call to x04abf before calling g01agf.

4
References

None.

5
Arguments

1:     xnobs – Real (Kind=nag_wp) arrayInput
On entry: the values to be plotted in the x-direction.
2:     ynobs – Real (Kind=nag_wp) arrayInput/Output
On entry: the values to be plotted in the y-direction.
On exit: the elements of y are sorted into descending order of magnitude.
3:     nobs – IntegerInput
On entry: the number of observations to be plotted.
Constraint: nobs1.
4:     isortnobs – Integer arrayOutput
On exit: the key to the descending order of the elements in array y, i.e., isorti contains the position of the value yi in the original array y, for i=1,2,,nobs.
5:     nstepx – IntegerInput
On entry: the number of steps (character positions) to be plotted in the x-direction. If the supplied value of nstepx is less than 10, the value 10 will be used by g01agf. The maximum value for nstepx is the number of character positions available on the chosen output device less 15, up to a maximum of 133. If nstepx exceeds 133 on input, the value 133 will be used by the routine.
6:     nstepy – IntegerInput
On entry: the number of steps (character positions) to be plotted in the y-direction. If the supplied value of nstepy is less than 10, the value 10 will be used by g01agf. There is no maximum value for nstepy, but you should bear in mind that nstepy+5 records (lines) of output are generated by the routine.
7:     ifail – IntegerInput/Output
On entry: ifail must be set to 0, -1​ or ​1. If you are unfamiliar with this argument you should refer to Section 3.4 in How to Use the NAG Library and its Documentation for details.
For environments where it might be inappropriate to halt program execution when an error is detected, the value -1​ or ​1 is recommended. If the output of error messages is undesirable, then the value 1 is recommended. Otherwise, if you are not familiar with this argument, the recommended value is 0. When the value -1​ or ​1 is used it is essential to test the value of ifail on exit.
On exit: ifail=0 unless the routine detects an error or a warning has been flagged (see Section 6).

6
Error Indicators and Warnings

If on entry ifail=0 or -1, explanatory error messages are output on the current error message unit (as defined by x04aaf).
Errors or warnings detected by the routine:
ifail=1
On entry, nobs=value.
Constraint: nobs1.
ifail=-99
An unexpected error has been triggered by this routine. Please contact NAG.
See Section 3.9 in How to Use the NAG Library and its Documentation for further information.
ifail=-399
Your licence key may have expired or may not have been installed correctly.
See Section 3.8 in How to Use the NAG Library and its Documentation for further information.
ifail=-999
Dynamic memory allocation failed.
See Section 3.7 in How to Use the NAG Library and its Documentation for further information.

7
Accuracy

Accuracy is limited by the number of plotting points available.

8
Parallelism and Performance

g01agf is threaded by NAG for parallel execution in multithreaded implementations of the NAG Library.
Please consult the X06 Chapter Introduction for information on how to control and interrogate the OpenMP environment used within this routine. Please also consult the Users' Note for your implementation for any additional implementation-specific information.

9
Further Comments

The time taken by g01agf may be expected to be approximately proportional to the product nobs×nstepx×nstepy.
No blank records are output before or after the plot.
You must make sure that it is permissible to write records containing nstepx characters to the current advisory message unit.

10
Example

The data relate to wheat and potato yields in 48 counties in England in 1936. The example illustrates the use of x04abf to set the logical unit number, used for the output of g01agf, to a specified value.

10.1
Program Text

Program Text (g01agfe.f90)

10.2
Program Data

Program Data (g01agfe.d)

10.3
Program Results

Program Results (g01agfe.r)

© The Numerical Algorithms Group Ltd, Oxford, UK. 2017