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Hi there,
How do I implement cubic regression? I.e. given a series of x-y data points, how do I find the coefficients:
y = ax^3 + bx^2 + cx + d
Am aware that if I differentiate twice, I get:
d2y/dsx2 = 6ax + 2b
so if I can numerically differentiate my x-y data twice, I can find constants a & b by linear regression.
How do I go about differentiating the data. And how do I find constants c & d?
Or is there a better approach?
http://en.wikipedia.org/wiki/Linear_regression
This gets into Linear Algebra.
Thanks for the reply.
>This gets into Linear Algebra.
I can do the linear regression bit. But...
how do I transform a cubic in order to determine all the constants?
This page can perhaps help you:
http://www.efunda.com/math/leastsqua...sqrmdcurve.cfm
it's linked from
http://www.efunda.com/math/leastsqua...astsquares.cfm
These pages seem good, there's a linear example as well.
To do this in MATLAB, use the polyfit() function.
why not just use the cubic regression from your TI-83 ? :cool:
>This page can perhaps help you:
Indeed yes, that helps. Thank you.
>why not just use the cubic regression from your TI-83 ?
Because I am writing a program to do it. :)