Epsilon

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jiban
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Epsilon

Post by jiban » Thu Aug 26, 2010 6:48 am

Can anyone tell me when I have to use epsilon rounding in floating point numbers ? What's the meaning of "The Judge data is prepared such that any good solution can use epsilon from 10^-7 to 10^-13" this kind of statements?

mf
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Re: Epsilon

Post by mf » Thu Aug 26, 2010 11:07 am

Floating point types have a finite precision, and so they typically represent values with some round-off error. You should add/subtract some small value (epsilon) during comparison of floats in order to tolerate this error. E.g. instead of "a < b", it's better to write "a < b - EPS", and instead of "a <= b" - "a < b + EPS".
What's the meaning of "The Judge data is prepared such that any good solution can use epsilon from 10^-7 to 10^-13" this kind of statements?
It probably only means that the judges have a solution which managed to produce the correct output using epsilon values in this range.

You can't pick an epsilon too small, because of underflow. if you're using a double type, it has a precision for about 15-16 digits (e.g. 1 + 1e-16 == 1), and so you can't pick an epsilon that's 10^15 - 10^16 times smaller than the magnitude of values that you're going to be dealing with.

And you obviously can't pick a large epsilon, or your program will start to behave incorrectly.

zobayer
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Re: Epsilon

Post by zobayer » Mon Jun 13, 2011 12:56 am

for double type, sometimes 0 is printed -0, idk why, but adding EPS with output helps to avoid it.
You should not always say what you know, but you should always know what you say.

Ranier
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Re: Epsilon

Post by Ranier » Mon Apr 18, 2016 9:51 am

mf wrote:Floating point types have a finite precision, and so they typically represent values with some round-off error. You should add/subtract some small value (epsilon) during comparison of floats in order to tolerate this error. E.g. instead of "a < b", it's better to write "a < b - EPS", and instead of "a <= b" - "a < b + EPS".
What's the meaning of "The Judge data is prepared such that any good solution can use epsilon from 10^-7 to 10^-13" this kind of statements?
It probably only means that the judges have a solution which managed to produce the correct output using epsilon values in this range.

You can't pick an epsilon too small, because of underflow. if you're using a double type, it has a precision for about 15-16 digits (e.g. 1 + 1e-16 == 1), and so you can't https://dudehung.com/vigrx-plus-review-results-2016 the VigRx Plus stuff with an epsilon that's 10^15 - 10^16 times smaller than the magnitude of values that you're going to be dealing with.

And you obviously can't pick a large epsilon, or your program will start to behave incorrectly.
Thanks MF, this made a lot of sense and was helpful as I was struggling with epsilon rounding.

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