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Well like the batman equations and equations for heart, I once saw a site that draws equation for whatever text you type....but now I can't find it. Does anybody know such a site? Also a general explanation how do they do it...I think they have to write equations for all characters from $a$ to $z$ manually then do some coordinate shift etc.

PS: If somebody has some matlab code to help then it will be awesome.

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    like in matlab f = @(x,y)((x.^2 + y.^2 -1)^3 - (x.^2) *(y.^3)); will draw a heart....so i want a function f(x,y) such that plot of f(x,y)=0 is some text(or looks like text)....2011-10-28

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Perhaps you meant that link: http://www.xamuel.com/inverse-graphing-calculator.php?phrase=Hello+World

[update, concerning your request for explanation]: Once you have a solution to define a plotting formula in the form $\small f(x,y)=0 $ and define the curve to be painted black if that equation is true, then you may combine many such formulas $\small f(x,y) \cdot g(x,y) \cdot h(x,y)=0 $ to draw combined pictures. (the multiplication implements the boolean OR: if any of the components is zero, draw a black point). The key is then to define some primitives, combine them to a letter (shifting coordinates appropriately), and combine that combinations to words, and ...

(Another example is at http://go.helms-net.de/math/fun/pdf/PdFdiscovery_ED.html ; I'd made some fun with an enthusiastic "fermatist" in the newsgroup sci.math one time )

(A bit more explanative is the following; here you can see the composition of the graph by its elements, although the logic is a bit different: click the top-left icon (that with th scribbled face) on http://go.helms-net.de/math/index.htm to see my first version of such a picture, when I was a schoolboy)

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    yeah,this is exactly what i was looking for..2011-10-28
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This can generally solved as an interpolation problem. Find points on the outline of the "image" you want to draw with a formula and use for example piecewise interpolation. Then you will get a formula that approximates the surface of your image.

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    FWIW: Fonts are often rendered with splines or Bézier curves, so this suggestion is quite near to the truth.2011-10-28