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How To Plot A Curve With Given Three Points?

by optics.tech
Tags: curve, plot, points
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optics.tech
#1
Aug8-11, 10:08 PM
P: 80
Hi everyone,

Can someone please tell me is there any mathematical equation/formula on ploting a curve with given three coordinates/points such as below image?

Thank you very much for your help

Op
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Ploting Curve.PNG  
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hotvette
#2
Aug8-11, 10:42 PM
HW Helper
P: 925
There are infinitely many curves you can draw through three points. The simplest method it to use a 2nd order polynomial (i.e a parabola). Just write out 3 equations using the values of x & y:

y1 = a x21 + b x1+ c
y2 = a x22 + b x2+ c
y3 = a x23 + b x3+ c

This is 3 equations in 3 unknowns (a,b,c) that can be solved by substitution.
uart
#3
Aug8-11, 11:29 PM
Sci Advisor
P: 2,751
As hotvette has already said, there are infinitely many curves you can draw through three points.

Two common cases in which the curve is uniquely specified by three points are the parabola and the circle. That is, if you assume it's a circle then such a circle is unique, and if you assume it's a parabola then such a parabola is unique.

JJacquelin
#4
Aug9-11, 12:52 AM
P: 756
How To Plot A Curve With Given Three Points?

if you assume it's a parabola then such a parabola is unique
No, there are an infinity of parabolas that can be draw through three points, each one with a different axial direction. Of course, il you asume a given direction for the axis, the parabola is unique.
optics.tech
#5
Aug9-11, 08:24 PM
P: 80
There are infinitely many curves you can draw through three points. The simplest method it to use a 2nd order polynomial (i.e a parabola). Just write out 3 equations using the values of x & y:

y1 = a x21 + b x1+ c
y2 = a x22 + b x2+ c
y3 = a x23 + b x3+ c

This is 3 equations in 3 unknowns (a,b,c) that can be solved by substitution.
What about if the amount of the points are nine pieces?

Will above equations can be continued from three to nine equations with similar pattern?

Does this curve is a kind of smooth and continue curve?
uart
#6
Aug10-11, 01:59 AM
Sci Advisor
P: 2,751
Quote Quote by optics.tech View Post
What about if the amount of the points are nine pieces?

Will above equations can be continued from three to nine equations with similar pattern?

Does this curve is a kind of smooth and continue curve?
If you want to extend this to an arbitrary number of points then you're probably looking for something more like a spline (piecewise fit). See: http://en.wikipedia.org/wiki/Spline_%28mathematics%29
agentredlum
#7
Aug10-11, 07:25 AM
P: 460
If all 3 point's are colinear then it can't be a circle or a parabola, unless the radius of the circle goes to infinity or the coefficient of x^2 goes to infinity or zero for the parabola. It can be many other things but the best representation is probably a straight line, unless you have some kind of 'exotic' application such as temperature changes over time.
mikeph
#8
Aug10-11, 08:42 AM
P: 1,212
For nine points I think you'll need a 9th order polynomial, so you'd get nine equations (and a headache). Something tells me the reasoning stems from the fundamental theorem of algebra, but I couldn't give you more detail than that.


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