How to find equation of curve if just graph is given

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Pranav
Pranav 2012-7-27
Hello All,
I have just graph with me in matlab and from that I have to find equation of curve. Can anybody help me to find that ?

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回答（1 个）

Conrad
Conrad 2012-7-27
You will have to make some assumptions about the functional form of the curve... for example if you know the curve is of the form y = b1 + b2*x + b3*x^2 + ...., you can solve for b by b = ((X'X)^-1)*X'*Y where X = [1 x x^2 ...].
Conrad
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John D'Errico
John D'Errico 2012-7-27
编辑：John D'Errico 2012-7-27
NO, NO, NO!!!!!!!! Don't teach people to use the normal equations, i.e., b = ((X'X)^-1)*X'*Y. Terrible numerically. Just silly when a better solution exists. You are squaring the condition number of the problem, so this is bad when the system is at all ill-conditioned. Then you are using inv on a problem where it is less than desirable.
b = X\Y;
Don't continue to propagate the bad things you learned.
Conrad
Conrad 2012-7-27
John, rather than just criticising I would prefer, as I am sure Pranav would as well, that you present your better solution.

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