Draw a circle in gnuplot

Here’s the content of the script I will use with gnuplot to make a graph of a circle using Cartesian coordinates. Save the file as ‘circle.gpt’ and run as a script with command ‘gnuplot circle.gpt’. Alternatively you could write the commands in gnuplot using the interactive mode.

set terminal png

set nokey
set xrange[-10:10]
set yrange[-10:10]

set output "circle.png"
set samples 100000
r = 5.0 ## radius 
a = 3.0 ## x shift
b = 4.0 ## y shift

f1(x) = sqrt(r**2 - (x-a)**2) - b
f2(x) = sqrt(r**2 - (x-a)**2) + b

plot f1(x) lw 3, -1*f2(x) lw 3 lt 1
 






Circle plotted with above script

For notation I followed the great handout available here: http://www.eclecticon.info/maths%20-%20geometry.htm — topic of the handout is Cartesian equation of a circle.

Explanation from Khan academy

https://www.khanacademy.org/math/geometry/xff63fac4:hs-geo-conic-sections/hs-geo-circle-expanded-equation/a/circle-equation-review

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