| Slide Number 1
Title Slide
Plotting functions
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Welcome to the tutorial on Plotting functions in gnuplot.
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| Slide Number 2
Learning Objectives
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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
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| Slide Number 3
Learning Objectives
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* 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.
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| Slide Number 3
System and Software Requirement
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To record this tutorial, I am using
- Debian Linux 9.3
- gnuplot 5.2.6
- gedit text editor 3.22
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| Slide Number 4
Pre-requisites
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To follow this tutorial,
- Learners must be familiar with high school level Mathematics.
- For pre-requisite gnuplot tutorials, please visit this site.
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| Press Ctrl Alt T
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Open a terminal by pressing Ctrl, Alt and T keys simultaneously.
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| Type cd Desktop and press Enter
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A terminal opens.
Change directory to Desktop as seen.
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| >gnuplot
Press Enter
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In the terminal, type gnuplot and press Enter.
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| Hover mouse near gnuplot prompt
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The prompt changes to gnuplot prompt.
To execute a command in the terminal, press Enter after typing it.
I will not mention this separately.
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| Press Ctrl shift K
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I will clear the terminal.
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| Type plot sin (x)
Press Enter
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Now type plot space sin (x)
Note that angle x is within parentheses.
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| Point to graphical window
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A graphical window with plot of sin(x) versus x appears on the screen.
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| Hover mouse on graph, axes.
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The limit of the Y axis is from minus 1 to plus 1.
And the X axis is from -10 to 10.
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| Type set grid
Press Enter
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Come back to the terminal and type the command set space grid.
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| Type replot
Press Enter
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Then type replot to see the grid in the graph.
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| Hold Ctrl and zoom in with mouse scroll
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Hold down the Control key and move the mouse scroll wheel to zoom in and zoom out.
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| Point to sin x and x
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Observe that sin x is zero when x is zero.
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| Show zoom in and out.
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Let us reset the limits of the axes as before.
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| Type reset
Press Enter
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To reset, type the command reset in the terminal, followed by replot.
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| Type replot
Press Enter
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Changes in the graph become visible only after executing the replot command.
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| Point to the legend
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Notice that the legend is on the top right side in the graph.
It is not clear and intersects the graph.
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| Point mouse on the legend.
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Let's increase y axis range, so that the graph line does not intersect the legend.
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| Type set yrange [-2:2]
Press Enter
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Type set space yrange space -2 colon 2 within square brackets.
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| Type set xrange [-20:20]
Press Enter
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I will also change x axis range.
Enter command, set space xrange space -20 colon 20 within square brackets.
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| Type replot
Press Enter
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Type replot to see the updated graph.
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|
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Now the changed graph limits are visible.
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| Point to the legend.
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The legend has moved up and does not intersect the data line anymore.
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| Type set key top left
Press Enter
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Type set space key space top space left to move the legend to the top left side.
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| Type replot
Press Enter
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Do not forget to replot to see the result.
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| Hover mouse next to axis font.
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Next, let's make the axes fonts larger.
I want to set them at size 14 and in Verdana style.
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| Type set tics font “Verdana, 14”
Press Enter
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Type this command as shown here, to change the font size and style.
Replot to see the result.
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| Hover mouse next to axis font.
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Notice the larger font size in Verdana style.
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| Type set xlabel 'x (angle)' font “Verdana, 14”
Press Enter
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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.
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| Type set ylabel 'sin (x)' font “Verdana, 14”
Press Enter
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To set y axis label as sin x, type the command, as shown here.
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| Only narration
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We are using the same font size and style for y axis too.
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| Type replot
Press Enter
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Type replot and press Enter.
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| Only narration
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Now, let’s see how to change the font in the legend.
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| Type set key font ",16"
Press Enter
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Type
set space key space font space within double quotes comma 16
This command sets the legend font size to 16.
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| Press Ctrl+Alt+K
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I will clear the terminal.
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| Type help fonts
Press Enter
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To access help documentation on fonts, type help space fonts.
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| Point mouse to cairo, gd and postscript
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Help command returns with 3 subtopics cairo, gd and postscript.
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| Type cairo
Press Enter
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I will type cairo to see the details and available options.
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| Only narration
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Similarly you may choose to use help for any command when using gnuplot.
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| Mouse in Help section
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You may pause the video and read the details given in the help section.
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| Press Ctrl C
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Once done, press Control and C keys to exit the help section.
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| Ctrl L in Ubuntu
Ctrl Shift K in Debian
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I will clear the screen.
I wish to add a title to my graph.
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| Type set title 'My first gnuplot'
Press Enter
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To add a title, type set title command, as shown here.
Followed by the title of the graph in single quotes.
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| Type set title font "verdana, 18"
Press Enter
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To set the title font, type the command as shown here.
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| Point to x axis
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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.
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| 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,)
>enter
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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.
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| Point mouse to ('2{/Symbol p}' and then to 2*pi
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This command places, Greek symbol pi, at the value of 3.14.
Label 2π is at position 6.28 on the X axis.
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| Point to 2π and 4π.
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Multiples of pi are placed at their respective positions.
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| Type help set xtics
Press Enter
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For more help on the formats of X tics, type the command help space set space xtics.
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| Press Ctrl C
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Press Ctrl and C keys to exit the help section.
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| I will clear the terminal.
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| Only narration
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It is also possible to add multiple functions on the same graph.
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| Type plot sin (x), cos (x)
Press Enter
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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 .
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| Point to the graph window
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Notice that the two functions are plotted together now.
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| Only narration
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Next, we will add sin (x) plus cos (x) function to the same graph.
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| Type plot sin(x), cos(x), sin(x) + cos(x)
Press Enter
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For this, type plot space sin(x) comma cos(x) comma sin(x) plus cos(x) .
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| Point to the graph window
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Notice that all 3 functions are plotted together on the same graph now.
Next, let’s learn how to get sin(x) data points into a file.
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| Only narration
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To get an ASCII column format output, set table command can be used.
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| Type set space table
Press Enter
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First type set space table.
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| Enter command plot sin(x) and press Enter
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Then type plot space sin(x).
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| Point to the screen
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An x y column data for sin(x) is generated on the screen.
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| Highlight first column
Highlight second column
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The first column is x data and the second column is y data.
They are the points of sin x versus x graph.
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| Press Ctrl+Alt+K
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I will clear the terminal.
We can save the output as a text file.
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| Type set table "table-sinx.txt".
Press Enter
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For this, type set space table space within double quotes sinx dot txt
Here sinx dot txt is the output filename.
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| Type plot sin(x)
Press Enter
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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,
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| Show screenshot of Desktop showing the file sinx.txt.
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The file is stored in the directory from where we opened gnuplot in the terminal.
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| Type unset table
Press Enter
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Type unset space table to exit the tabular output mode.
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| Enter q
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Then type quit or q to quit gnuplot.
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| Slide Number 6
Summary
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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 the graph
- Added axis labels and graph title
- Changed font style and size and
- Saved the data points to a file
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| Slide Number 7
Assignment
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As an assignment, plot the following functions:
- tan x
- x squared and
- x minus three squared
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| Completed assignment
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Your completed assignment should look like this.
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| Slide Number 8
Spoken Tutorial Project
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This video summarises the Spoken Tutorial Project
Please download and watch it.
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| Slide Number 9
Spoken Tutorial workshops
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We conduct workshops using spoken tutorials and give certificates.
Please write to us.
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| Slide Number 10
Forum for specific questions:
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Post your timed queries in the forum.
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| Slide Number 11
AcknowledgemenT
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Spoken Tutorial Project is funded by NMEICT, MHRD, Government of India.
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This is Rani from IIT, Bombay. Thank you for joining.
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