ahmed.abouraya

12-11-2009, 06:14 AM

if i have a set of 9 points how can i get the function???

View Full Version : find the function

ahmed.abouraya

12-11-2009, 06:14 AM

if i have a set of 9 points how can i get the function???

Yomboprime

12-11-2009, 12:38 PM

If you have Px,y(1) to Px,y(N) points with x and y values, then

the linear function is F(x):

if x is between Px(i) and Px(i+1), then

a = ( x - Px(i) ) / ( Px(i+1) - Px(i) )

F(x)= Py(i) * a + Py(i+1) * ( 1 - a )

else if x < Px(1) then F(x) = Px(1)

else if x > Px(N) then F(x) = Px(N)

the linear function is F(x):

if x is between Px(i) and Px(i+1), then

a = ( x - Px(i) ) / ( Px(i+1) - Px(i) )

F(x)= Py(i) * a + Py(i+1) * ( 1 - a )

else if x < Px(1) then F(x) = Px(1)

else if x > Px(N) then F(x) = Px(N)

Rosario Leonardi

12-11-2009, 01:23 PM

If you want a polynomial function that pass through every point you can use the Newton polynomial function.

http://en.wikipedia.org/wiki/Newton_polynomial

or the Lagrange form

http://en.wikipedia.org/wiki/Lagrange_polynomial

But beware, with 9 point you can get a 9 grade polynomial that will rise very fast for number outside the interval of your point.

Otherwise if you want an approximation of the formula and you already know the distribution of your point you can use a least squares method.

http://en.wikipedia.org/wiki/Least_squares

http://en.wikipedia.org/wiki/Newton_polynomial

or the Lagrange form

http://en.wikipedia.org/wiki/Lagrange_polynomial

But beware, with 9 point you can get a 9 grade polynomial that will rise very fast for number outside the interval of your point.

Otherwise if you want an approximation of the formula and you already know the distribution of your point you can use a least squares method.

http://en.wikipedia.org/wiki/Least_squares

ahmed.abouraya

12-12-2009, 03:55 PM

it worked thanks alot

Powered by vBulletin® Version 4.2.2 Copyright © 2015 vBulletin Solutions, Inc. All rights reserved.