Can You Find the Function of a Random Curve on Graph Paper?

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Discussion Overview

The discussion explores the feasibility of determining a mathematical function that defines a random curve drawn on graph paper, with a focus on smooth curves and the potential for complex curves. Participants consider various methods and approaches for approximating these curves.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions whether it is possible to find a function for a random smooth curve drawn on graph paper, including the possibility of complex curves.
  • Another participant suggests that the Fourier transform provides a method for this task, referencing a video for further illustration.
  • A different participant proposes that by selecting multiple points on the curve, one can use polynomial interpolation to approximate the function, acknowledging that this may not yield the exact function if only part of the graph is drawn.
  • One participant introduces cubic splines as a common method used in computer graphics to create smooth curves through a set of points, noting that separate splines would be needed for the real and imaginary parts of complex curves.
  • It is mentioned that there are infinitely many smooth curves that can pass through a given set of points, and cubic splines tend to produce visually appealing results.

Areas of Agreement / Disagreement

Participants express differing views on the methods for approximating curves, with some advocating for polynomial interpolation and others for cubic splines. No consensus is reached on the best approach or the feasibility of finding a definitive function for arbitrary curves.

Contextual Notes

Participants acknowledge limitations in their methods, such as the dependency on the number of points chosen and the nature of the curves being approximated. There is also an implicit assumption that the curves are smooth.

thetexan
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is it possible to draw a random curve on a piece of graph paper and find the function that defines that curve? Assuming smooth curves.

And if so,is it possible to do so with complex curves?

tex
 
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thetexan said:
is it possible to draw a random curve on a piece of graph paper and find the function that defines that curve? Assuming smooth curves.
Approximately, yes. You can choose as many points ##(x_i,y_i)## you like - the more the better - say ##n+1## many, then set ##p(x)=a_0x^n+a_1x^{n-1}+\ldots +a_{n-1}x+a_n## and solve ##p(x_i)=y_i## for the coefficients ##a_i##. That doesn't give you the correct answer in case your function is defined otherwise and you only drew a certain part of the graph, but it is a good approximation for what you have drawn.
And if so,is it possible to do so with complex curves?
How do you sketch a four dimensional graph, ##(Re(x_i)+i\cdot Im(x_i)\; , \;Re(y_i)+i\cdot Im(y_i))\,?##
 
In general the most common approach, the one that is used in computer graphics to go through an arbitrary set of points, is cubic splines. Between each pair of points is a different cubic polynomial ##y = a_0 + a_1 x + a_2 x^2 + a_3 x^3## with different coefficients. There are four free coefficients on each segment which are chosen so that the curves pass through the points and also meet smoothly.

For a complex curve, you'd use separate splines for the real and imaginary parts. I've done that on a number of occasions in fact.

Similarly, for a curve that doubles back on itself like a circle or something more complicated, you would use separate cubics for ##x## and ##y##.

There are infinitely many smooth curves that go through a given set of points, since you aren't restricting what happens between those points. But cubic splines usually give a natural looking curve, one that follows the points in a way you would expect.
 
Quiet helpful. thank you!
 

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