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# Quadratic curve fitting!

 P: n/a Number One: ========= I know its a 100% offline post.But seeing the diversity of the domain from which people are participating, I would like to post this question here.Pardon me.At the least, u can guide me to the proper newsgroup.Thanks. Number Two: ========= I want to draw a curve for a set of observations(i.e, x,y pairs) using Quadratic fit using Least Square method. I do not what is the step1, step2, step 3 i mean alogorithm for this process.Any helps will be gratefully appreciated. Regards, Vinodh Kumar P Jul 19 '05 #1
5 Replies

 P: n/a "Vinodh Kumar" wrote in message news:bh**********@news.mch.sbs.de... Number One: ========= I know its a 100% offline post. So, you don't even have an excuse. But seeing the diversity of the domain from which people are participating, I would like to post this question here.Pardon me.At the least, u can guide me to the proper newsgroup.Thanks. I wouldn't have a clue. Did you try looking for a group with 'algorithm', 'math' or related term, or did you just decide to ask a completely off-topic question as your first step? Number Two: ========= I want to draw a curve for a set of observations(i.e, x,y pairs) using Quadratic fit using Least Square method. I do not what is the step1, step2, step 3 i mean alogorithm for this process.Any helps will be gratefully appreciated. Completely off-topic, which you already know. So why bother asking? DW Jul 19 '05 #2

 P: n/a "Vinodh Kumar" wrote in message news:bh**********@news.mch.sbs.de... Number One: ========= I know its a 100% offline post.But seeing the diversity of the domain from which people are participating, I would like to post this question here.Pardon me.At the least, u can guide me to the proper newsgroup.Thanks. Number Two: ========= I want to draw a curve for a set of observations(i.e, x,y pairs) using Quadratic fit using Least Square method. I do not what is the step1, step2, step 3 i mean alogorithm for this process.Any helps will be gratefully appreciated. You are most likely to get a good and peer reviewed answers if you post the question to a newsgroup where your question is topical. In this case that would be comp.graphics.algorithms -- Peter van Merkerk peter.van.merkerk(at)dse.nl Jul 19 '05 #3

 P: n/a Vinodh Kumar wrote: Number One: ========= I know its a 100% offline post.But seeing the diversity of the domain from which people are participating, I would like to post this question here.Pardon me.At the least, u can guide me to the proper newsgroup.Thanks. Number Two: ========= I want to draw a curve for a set of observations(i.e, x,y pairs) using Quadratic fit using Least Square method. I do not what is the step1, step2, step 3 i mean alogorithm for this process.Any helps will be gratefully appreciated. Regards, Vinodh Kumar P Well, i don't know what are your real aims. We use least square method to fit with a model curve. By example, you can by this method find the straight line who is the nearest from a set of points. It is very used in physics when you want to find numerically the parameters of a linear law. You can also use least square method to find the nearest parabole, cubic ... curve, which is the nearest from your points. You compute by this way the coefficients a,b,c so that y=a x² + b x +c is the nearest parabol from your points. Then you have to minimize the functionnal J = Sum_i( (y_i - a*x_i²+ b*x_i +c)^2) where (x_i,y_i) is the set of points If your aim is to smooth a set of edges, you can use smooth techniques like splines. Especially cubic splines are very nice. You ensure by using cubic splines that your curve will pass by your sets of points, and the curve is smooth. I joined a documentation about splines http://kr.cs.ait.ac.th/~radok/math/mat7/step28.htm http://math.arizona.edu/~restrepo/47...ea/node35.html -- Marc Durufle Inria Rocquencourt Tel : 01 39 63 56 27 -------------------------- Jul 19 '05 #4

 P: n/a "Vinodh Kumar" wrote in message news:bh**********@news.mch.sbs.de... Number One: ========= I know its a 100% offline post.But seeing the diversity of the domain from which people are participating, I would like to post this question here.Pardon me.At the least, u can guide me to the proper newsgroup.Thanks. Number Two: ========= I want to draw a curve for a set of observations(i.e, x,y pairs) using Quadratic fit using Least Square method. I do not what is the step1, step2, step 3 i mean alogorithm for this process.Any helps will be gratefully appreciated. Regards, Vinodh Kumar P It is very OT in here... but I would suggest using Newton's interpolation formula to work out the polynomial. Look Newton interpolation formula up in google and it should give you enough information. If you need anymore help, email me and I will do my best. HTH, S. Armondi Jul 19 '05 #5

 P: n/a It is very OT in here... but I would suggest using Newton's interpolation formula to work out the polynomial. Look Newton interpolation formula up in google and it should give you enough information. If you need anymore help, email me and I will do my best. HTH, S. Armondi I hope you won't have lots of points because classical Lagrangian interpolation (we call also Newton) gives a poor approximation when the degree of polynoms increase. You get oscillations and it is why we prefer to use cubic splines :-) You can also use lagrangian polynomials on subsets of 3 or 4 points, but you will have discontinuities in your curve. Anyway, it works... -- Marc Durufle Inria Rocquencourt Tel : 01 39 63 56 27 -------------------------- Jul 19 '05 #6

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