Hello,

On Wednesday, February 23, 2011 5:25:45 AM UTC+1, Ronan Lamy wrote:
>
> The conventional definition of the order of the expansion is that it's
> the degree of the last term included in the polynomial approximation, so
> one less than the order of the excluded terms. Your example is a
> second-order expansion, because it gives a second-order approximation.
>
I agree up to a small detail. I think the usual way is to write e.g. f(x) = 
cos(x) as
f(x) = 1 - 0.5 x^2 + O(4).
Note the O(4) term. I think this is usually done to reflect the fact that in 
this expansion cannot contain uneven powers of x as cos(x) is an even 
function. Though competitors such as Mathematica are not that smart, I think 
a behaviour like this might be worth considering.

Cheers

Alex

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