Difference between revisions of "Gnuplot/C2/Plotting-functions/English"

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Revision as of 11:49, 18 October 2019

Visual Cue Narration
Slide Number 1

Title Slide Plotting functions

Welcome to the tutorial on Plotting functions in gnuplot.
Slide Number 2

Learning Objectives

In this tutorial we will learn,
  • Plot and replot commands for 2D plotting
  • Plot three functions: sin(x), cos(x) and sin(x) plus cos(x)
  • Draw grid and set limits
  • Zoom in and zoom out of a plot
Slide Number 3

Learning Objectives

  • Add axis labels and graph title
  • Change font style and size
  • Add Greek symbols
  • Set axis tick marks and
  • Save the data points to a file
Slide Number 4

System and Software Requirement

To record this tutorial, I am using
  • Debian Linux 9.3
  • gnuplot 5.2.6 and
  • gedit text editor 3.22.0
Slide Number 5

Pre-requisites

To follow this tutorial,
  • Learner must be familiar with high school level Mathematics
  • For prerequisite gnuplot tutorials, please visit this site
Press Ctrl + Alt + T . Open a terminal by pressing Ctrl, Alt and T keys simultaneously.
Type cd Desktop and press Enter. A terminal opens.

Change directory to Desktop as seen.

Type gnuplot and press Enter. In the terminal, type gnuplot and press Enter.
Hover mouse near gnuplot prompt. The prompt changes to gnuplot prompt.

To execute a command in the terminal, press Enter after typing it.

I will not mention this separately.

Press Ctrl+Shift+K. I will clear the terminal.
Type plot sin(x) and Press Enter. Now type plot space sin(x).

Note that angle x is within parentheses.

Point to graphical window. A graphical window with plot of sin(x) versus x appears on the screen.
Hover mouse on graph, axes. The limit of Y axis is from minus 1 to plus 1.

And X axis is from -10 to 10.

Type set grid and press Enter. Come back to the terminal and type the command set space grid.
Type replot and press Enter Then type replot to see the grid in the graph.
Hold Ctrl and zoom in with mouse scroll. Hold down the Control key and move the mouse scroll wheel to zoom in and zoom out.
Point to sin x and x. Observe that sin x is zero when x is zero.
Show zoom in and out. Let us reset the limits of the axes as before.
Type reset and press Enter. To reset, type the command reset in the terminal, followed by replot.
Type replot and press Enter. Changes in the graph become visible only after executing the replot command.
Point to the legend. Notice that the legend is on the top right side in the graph.

It is not clear and intersects the graph.

Point mouse on the legend. Let's increase y axis range, so that the graph line does not run through the legend.
Type set yrange [-2:2] and press Enter. Type set space yrange space -2 colon 2 within square brackets.
Type set xrange [-20:20] and

Press Enter.

I will also change x axis range.

Enter command, set space xrange space -20 colon 20 within square brackets.

Type replot and

Press Enter

Type replot to see the updated graph.
Cursor on the graph. Now the changed graph limits are visible.
Point to the legend. The legend has moved up and does not intersect the data line anymore.
Type set key top left and press Enter Type set space key space top space left to move the legend to the top left side.
Type replot and press Enter. Do not forget to replot to see the result.
Hover mouse next to axis font. Next, let's make the axes fonts larger.

I want to set them at size 14 and in Verdana style.

Type set tics font “Verdana, 14” and press Enter. Type this command as shown here, to change the font size and style.

Replot to see the result.

Hover mouse next to axis font. Notice the larger font size in Verdana style.
Type set xlabel 'x (angle)' font “Verdana, 14”.

Press Enter

Let's set x axis label as x angle.

Type the command as shown here.

Here we are specifying the label, font style and size in a single command.

Type set ylabel 'sin (x)' font “Verdana, 14” and press Enter. To set y axis label as sin x, type the command, as shown here.
Cursor on the terminal. We are using the same font size and style for y axis too.
Type replot and press Enter Type replot and press Enter.
Cursor on the graph. Now, let’s see how to change the font in the legend.
Type set key font ",16" and

Press Enter

Type

set space key space font space within double quotes comma 16 .

This command sets the legend font size to 16.

Press Ctrl+Alt+K. I will clear the terminal.
Type help fonts and press Enter To access help documentation on fonts, type help space fonts.
Point mouse to cairo, gd and postscript Help command returns with 3 subtopics cairo, gd and postscript.
Type cairo and press Enter I will type cairo to see the details and available options.
Cursor on the terminal. Similarly you may choose to use help for any command when using gnuplot.
Mouse in Help section. You may pause the video and read the details given in the help section.
Press Ctrl C. Once done, press Control and C keys to exit the help section.
Ctrl+L in Ubuntu and Ctrl+Shift+K in Debian. I will clear the screen.

I wish to add a title to my graph.

Type set title 'My first gnuplot' and press Enter. To add a title, type set title command, as shown here.

Followed by the title of the graph in single quotes.

Type set title font "verdana, 18" and press Enter. To set the title font, type the command as shown here.
Point to x axis. In the sinx versus x plot, dimensions of x axis is angle.

Hence we may want to label X axis in terms of angle, π.

In the terminal, type,

set xtics ('-4{/Symbol p}' -4*pi,'-3{/Symbol p}' -3*pi,'-2{/Symbol p}' -2*pi,

'-{/Symbol p}' -pi, 0, '{/Symbol p}' pi,

'2{/Symbol p}' 2*pi, '3{/Symbol p}' 3*pi, '4{/Symbol p}' 4*pi,) and press Enter.

To change X ticks to angle, type the following command as shown on the screen.

Here we are using the Greek alphabet pi and setting its position.

Point mouse to ('2{/Symbol p}' and then to 2*pi. This command places, Greek symbol pi, at the value of 3.14.

Label 2π is at position 6.28 on the X axis.

Point to 2π and 4π. Multiples of pi are placed at their respective positions.
Type help set xtics and press Enter. For more help on the formats of x tics, type the command help space set space xtics.
Press Ctrl C. Press Ctrl and C keys to exit the help section.
Press Ctrl+Shift+K in Debian. I will clear the terminal.
Cursor on the terminal. It is also possible to add multiple functions on the same graph.
Type plot sin(x), cos (x) and press Enter. To plot sin x and cos x on the same graph, separate the functions by a comma.

Type plot space sin x comma cos x.

Make sure that the angle x, is within parentheses .

Point to the graph window. Notice that the two functions are plotted together now.
Cursor on the terminal. Next, we will add sin (x) plus cos (x) function to the same graph.
Type plot sin(x), cos(x), sin(x) + cos(x) and press Enter. For this, type plot space sin(x) comma cos(x) comma sin(x) plus cos(x) .
Point to the graph window. Notice that all 3 functions are plotted together on the same graph window.

Next, let’s learn how to get sin(x) data points into a file.

Cursor on the terminal. To get an ASCII column format output, set table command can be used.
Type set space table and press Enter. First type set space table.
Enter command plot sin(x) and press Enter. Then type plot space sin(x).
Point to the screen An x y column data for sin(x) is generated on the screen.
Highlight first column.

Highlight second column.

The first column is x data and the second column is y data.

They are the points of sin x versus x graph.

Press Ctrl+Alt+K I will clear the terminal.

We can save the output as a text file.

Type set table "table-sinx.txt" and press Enter. For this, type set space table space within double quotes sinx dot txt.

Here sinx dot txt is the output filename.

Type plot sin(x) and press Enter. Then, type plot space sin(x).

The output is saved to the file sin x dot txt.

The data is not seen on the screen.

Show screenshot of Desktop showing the file sinx.txt. The file is stored in the directory from where we opened gnuplot in the terminal.
Type unset table and press Enter. Type unset space table to exit the tabular output mode.
Enter the command quit. Then type quit or q to quit gnuplot.
Slide Number 6

Summary

Let’s summarize.

In this tutorial,

  • we plotted 2D graphs of functions.

We also

  • Added grid and set limits
  • Zoomed in and zoomed out of a plot
  • Added axis labels and graph title
  • Changed font style and size

and

  • Saved the data points to a file
Slide Number 7

Assignment

As an assignment, plot the following functions:
  • tan x
  • x squared

and

  • x minus three squared
Show Completed assignment. Your completed assignment should look like this.
Slide Number 8

Spoken Tutorial Project

This video summarises the Spoken Tutorial Project.

Please download and watch it.

Slide Number 9

Spoken Tutorial workshops

We conduct workshops using spoken tutorials and give certificates.

Please write to us.

Slide Number 10

Forum for specific questions:

Post your timed queries in the forum.
Slide Number 11

Acknowledgement

Spoken Tutorial Project is funded by NMEICT, MHRD, Government of India.
This is Rani from IIT, Bombay. Thank you for joining.

Contributors and Content Editors

Madhurig, Ranipv076

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