My Math Forum Need help to found a formula for a data serial

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 May 1st, 2011, 03:16 PM #1 Newbie   Joined: May 2011 Posts: 6 Thanks: 0 Need help to found a formula for a data serial Hello first time here, and to be honest i m here because i need help. I have a data serie : 100 0.12 200 0.25 300 0.42 400 0.68 500 1.08 600 1.5 700 1.83 800 2.12 900 2.51 1000 3.09 1100 3.72 1200 4.2 1300 4.64 1400 5.21 1500 6.07 1600 6.99 1700 7.71 1800 8.35 1900 9.21 2000 10.48 2100 11.85 2200 12.92 2300 13.87 2400 15.13 2500 17.02 2750 21.31 3000 26.69 3250 33.07 3500 41.03 3750 50.51 4000 61.96 4250 75.71 4500 92.18 4750 111.9 5000 135.46 5250 163.58 5500 197.06 5750 236.93 6000 280.42 6250 334.76 6500 396.85 6750 467.43 7000 547.32 7250 637.31 7500 738.28 7750 873.75 8000 1004.9 8250 1142.96 8500 1289.66 8750 1442.97 9000 1604.53 9250 1772.41 9500 1948.16 9750 2129.93 10000 2319.2 10250 2514.19 10500 2716.29 10750 2923.82 11000 3138.08 11250 3357.48 11500 3583.23 11750 3813.81 12000 4050.37 12250 4291.47 12500 4538.16 12750 4789.1 13000 5045.25 13250 5305.34 13500 5570.27 13750 5838.85 14000 6111.88 14250 6388.27 14500 6668.74 14750 6952.25 i ploted the numbers in excel, i created a trendline but now i m not able to found a general formula for this serial. Excel give me a function like: y = 6E-21x6 - 3E-16x5 + 4E-12x4 - 2E-08x3 + 6E-05x2 - 0.0543x + 12.34 but it don t works. If someone can help me about....... Dc
 May 2nd, 2011, 07:51 AM #2 Newbie   Joined: May 2011 Posts: 6 Thanks: 0 Re: Need help to found a formula for a data serial any help?
 May 3rd, 2011, 03:29 PM #3 Member   Joined: Jul 2009 From: New Jersey Posts: 65 Thanks: 0 Re: Need help to found a formula for a data serial Try doing a spline
 May 3rd, 2011, 05:31 PM #4 Newbie   Joined: Apr 2011 Posts: 5 Thanks: 0 Re: Need help to found a formula for a data serial Hi dendricala, I did a quadratic regression on my TI-84+ calculator with every fifth of your data points. The calculator gave me the following function: y=0,000050749347026081x^2+-0,29690681072548x+271,2427198859 This is pretty accurate (R^2=0,9976). Excel only has limited regression possibilities as far as I know. I am also doing regressions for my bachelor thesis in micro economics. Here is a link to the excel file with your data (grouped), a graph (plot) of the data and the function i found. LINKY: http://www.2shared.com/file/qX-z2PtD/Qu ... thfor.html Best regards thenarfer (from Norway)
 May 5th, 2011, 09:37 PM #5 Newbie   Joined: May 2011 Posts: 6 Thanks: 0 Re: Need help to found a formula for a data serial hello a lot. I did a try, but i m sure i m very impared also to copy a formula...... let consider the first couple of data: x y 100 0.12 i need to change x with 100 in your equation =(0,000050749347026081*100)^2-0,29690681072548*100+271,2427198859 the result is 248.2736775 i m sure i m doing somenthing wrog !!!!
 May 8th, 2011, 09:27 PM #6 Newbie   Joined: May 2011 Posts: 6 Thanks: 0 Re: Need help to found a formula for a data serial it s against the rule bump my post????
 May 8th, 2011, 10:54 PM #7 Senior Member   Joined: Jun 2010 Posts: 618 Thanks: 0 Re: Need help to found a formula for a data serial dendricala, If you're going to bump your post, you have to be a bit more subtle about it, or else add some spice to it. Maybe try something really suave, like saying "I'm sorry, I think the 27th line in my long list of number should read 3000 26.66, not 3000 26.69, really sorry about that!" I think that would be more effective in getting people's attention. -Ormkärr-
 May 9th, 2011, 10:15 AM #8 Newbie   Joined: May 2011 Posts: 6 Thanks: 0 Re: Need help to found a formula for a data serial opps you right i apology
 May 12th, 2011, 05:14 AM #9 Newbie   Joined: May 2011 Posts: 6 Thanks: 0 Re: Need help to found a formula for a data serial look like i posted a real difficult problem.
 May 12th, 2011, 11:58 AM #10 Senior Member   Joined: Jun 2010 Posts: 618 Thanks: 0 Re: Need help to found a formula for a data serial dendricala, Did the work and suggestions of the previous posters not help? I don't really understand what you are after here. Do you want a polynomial "best fit" or some other regression, or an equation which gives exactly your values at the prescribed points? You will probably have to compromise one way or the other---either get a well-fitting curve, or else pass through all your points with possibly horrible intermediate behavior. Did you look at thenarfer's link? -Ormkärr-

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