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From |
Aaron Kirkman <ak5791@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Generate a random double between -1 and 1 |

Date |
Sun, 2 Sep 2012 16:09:48 -0500 |

Hi Steve, Good point. My number theory was a bit off in my original logic, and the blog post Nick linked to clears all that up. Thank you, Aaron On Sun, Sep 2, 2012 at 3:50 PM, Steve Samuels <sjsamuels@gmail.com> wrote: > > Your statement that >> "...multiplying 2 * runiform() excludes half the >> possible values between -1 and 1." > is incorrect, as the limits of -1 + 2*runiform() are -1 + 2*0 = -1, and -1 +2*1 = +1. > > > Steve > > > > On Sep 2, 2012, at 3:45 PM, Nick Cox wrote: > > See <http://blog.stata.com/2012/08/29/using-statas-random-number-generators-part-3-drawing-with-replacement/> > and prequels. > > Nick > > On Sun, Sep 2, 2012 at 8:26 PM, Aaron Kirkman <ak5791@gmail.com> wrote: >> I have a situation where I need to generate random real numbers >> between -1 and 1, and I'm wondering if there is a better way to >> accomplish this. Right now, I use this: >> >> clear >> set obs 100000000 >> gen double eps = -1 + 2 * runiform() >> summ eps >> >> While this is probably acceptable, as the theoretical mean is 0, it's >> problematic because multiplying 2 * runiform() excludes half the >> possible values between -1 and 1. Is there a built-in way to do this >> in a way that won't exclude values, or is this method sufficient? In >> practice, I may generate as few as 30 random numbers and as many as >> 100,000,000 (if that's relevant). > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > > > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: Generate a random double between -1 and 1***From:*Aaron Kirkman <ak5791@gmail.com>

**Re: st: Generate a random double between -1 and 1***From:*Nick Cox <njcoxstata@gmail.com>

**Re: st: Generate a random double between -1 and 1***From:*Steve Samuels <sjsamuels@gmail.com>

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