The Monkey Brain
An ascii implicit function plotter

Type in a mathematical expression in $x$ and $y$ into the input box above to plot it in ascii. The program expects an expression equal to zero, so if you want to plot $y = \sin(x)$, you would instead move everything to the left hand side, and enter $y - \sin(x)$ into the prompt.

What can you put in? The expression is parsed using math.js, so it can take most of these math.js functions, such as the trigonometric functions, log, exp, as well as interesting things like gcd and sign. There are some quirks with their language, so if you run into any trouble, it is best to be explicit. I can type $y - 2x$ and it would understand I want to multiply $2$ by $x$, but I can’t type $y - x(x-1)$ because the parentheses makes it think that I am trying to invoke a (nonexistent) function named $x$, and instead I have to put in $x*(x -1)$.

Under the hood, I rolled my own marching squares algorithm in javascript.

One interesting thing about doing this in ascii is that it’s such low-resolution that any rough edges in the code become really obvious. For instance, if you plot $x^2 + y^2 - 1$, the circle is lumpy for some reason.

Another fun glitch caused by the low resolution is that you can see aliasing. Plot $y - \sin(2x)$, then increase the factor of $2$. Around $5$ it starts to look weird, and at $y - \sin(8x)$ it is totally borked.

For bonus points, since the lines are drawn as “o”s, imagine a ghost vocalizing anything that you plot. How spooky – it is the ghost of algebraic geometry!

Source code is here.



The Monkey Brain is Sam Zhang's interactive blog of mathematical curiosities.

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