# How to select a sensible tolerance when making approximations in MATLAB

I'm approximating $\pi$ using a series in MATLAB. I can approximate to within a relative error of $3\times 10^{-10}$ of MATLAB's built-in value. How would I choose a sensible tolerance for my approximation? Would it possibly relate to machine epsilon?

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Which series? ${}$ –  Ｊ. Ｍ. Oct 5 '11 at 15:48
$1 - 1/3 + 1/5 - 1/7 + ...$ –  kobrien Oct 5 '11 at 16:03
I'm afraid I do. I want to compare it to Matlab's built-in value for pi for a varying number of terms in this series. –  kobrien Oct 5 '11 at 16:10
The usual criterion is to stop when the $k$-th term is less than the current partial sum times eps. –  Ｊ. Ｍ. Oct 5 '11 at 16:20
Hmm, change that to "absolute value of the $k$-th term"... –  Ｊ. Ｍ. Oct 5 '11 at 16:26