# How do you calculate the decimal expansion of an irrational number?

Just curious, how do you calculate an irrational number? Take $\pi$ for example. Computers have calculated $\pi$ to the millionth digit and beyond. What formula/method do they use to figure this out? How does it compare to other irrational numbers such as $\varphi$ or $e$?

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Minor aside: your question is not "how do you calculate an irrational number", but "how do you calculate the decimal expansion of an irrational number". –  Hurkyl May 20 '12 at 12:20

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