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function.md

@@ -82,6 +82,8 @@ Functions commonly used in mathematics range from the trivial ones (such as the
 - **[Dirac delta function](unit_impulse.md)**: Function representing infinitely short impulse with unit energy.
 - TODO
 
+{ Playing around with plotting 2D functions (functions with 2 parameters) is very fun, you can create beautiful pictures with very simple formulas. I once created a tool for this (just some dirty page with JavaScript) and found quite nice functions, for example: `gaussian_curve((x^2) mod (abs(sin(x + y)) + 0.001) + (y^2) mod (abs(sin(x - y)) + 0.001))` plotted from [-3,-3] to [3,3] (plot with amplitude set to range from white to black by given minimum and maximum in the given area). ~drummyfish }
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 ## Programming Functions
 
 In programming the definition of a function is less strict, even though some languages, namely [functional](functional.md) ones, are built around purely mathematical functions -- for distinction we call these strictly mathematical functions **pure**. In traditional languages functions may or may not be pure, a function here normally means a **subprogram** which can take parameters and return a value, just as a mathematical function, but it can further break some of the rules of mathematical functions -- for example it may have so called **[side effects](side_effect.md)**, i.e. performing additional actions besides just returning a number (such as modifying data in memory which can be read by others, printing something to the screen etc.), or use randomness and internal states, i.e. potentially returning different numbers when invoked (called) multiple times with exactly the same arguments. These functions are called **impure**; in programming a *function* without an adjective is implicitly expected  to be impure. Thanks to allowing side effects these functions don't have to actually return any value, their purpose may be to just invoke some behavior such as writing something to the screen, initializing some hardware etc. The following piece of code demonstrates this in [C](c.md):