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From |
annoporci <annoporci@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: rounding the minimum of a negative number |

Date |
Thu, 10 Jan 2013 22:19:36 +0800 |

Thanks Nick for these precisions.

If you want _display_ to a fixed number of decimal places, that is ultimately a question of formatting and not a problem of numerics.

Yes. I guess another way of expressing my puzzlement is that Stata does not display, by default, to a greater number of decimal places. I don't know anything about this, but in Python, for instance, according to the documentation: "On a typical machine running Python, there are 53 bits of precision available for a Python float." And, to quote more: If Python were to print the true decimal value of the binary approximation stored for 0.1, it would have to display: 0.1000000000000000055511151231257827021181583404541015625 So that's still quite a few zeros after the first 1. And if Stata had displayed something like -1.980000009999 for 1.9810, I would not have been puzzled. I do have one last question and then I'll consider the matter closed: Would I get a more accurate approximation of "-1.981" with Stata if I input "-1.981000000001" than if I input "-1.981" ? in the sense that it would "force" Stata to store the zeros after 981? (or am I misunderstanding the whole issue?) Thanks Nick, -- Patrick Toche. References: http://docs.python.org/2/tutorial/floatingpoint.html On Thu, 10 Jan 2013 20:15:45 +0800, Nick Cox <njcoxstata@gmail.com> wrote:

I don't think that is a clear specification of what Stata is doing (it doesn't "make up its own digits") or of what it should, in your view, do instead. If you want _display_ to a fixed number of decimal places, that is ultimately a question of formatting and not a problem of numerics. That is, display %3.2 f 1 + 98/100 will ensure that you see "1.98" and this last step is in essence string manipulation with numeric characters. But all that is done by (e.g.) scalar foo = 1.98 is putting a binary approximation of 1.98 in a scalar. Adding bits will change the accuracy of the approximation (only). Nick

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**Follow-Ups**:**Re: st: rounding the minimum of a negative number***From:*Maarten Buis <maartenlbuis@gmail.com>

**Re: st: rounding the minimum of a negative number***From:*Nick Cox <njcoxstata@gmail.com>

**References**:**st: rounding the minimum of a negative number***From:*annoporci <annoporci@gmail.com>

**Re: st: rounding the minimum of a negative number***From:*Nick Cox <njcoxstata@gmail.com>

**Re: st: rounding the minimum of a negative number***From:*annoporci <annoporci@gmail.com>

**Re: st: rounding the minimum of a negative number***From:*Nick Cox <njcoxstata@gmail.com>

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