machine eps related query

2020 12 29
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更新时间：2020 12 29
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1 + eps > 1
ans =
logical
1
% as expcted
1 + eps
ans =
1.000000000000000
% unexpected, and indeed
1+2.5*eps
ans =
1.000000000000000
any help appreciated

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Ameer Hamza
Ameer Hamza 2020-12-29

0 个投票

It happens because of finite precision of double() precision datatype: https://en.wikipedia.org/wiki/Double-precision_floating-point_format. Also, because of the fact that MATLAB only prints 16 digits by default, the remaining digits after conversion are not shown (double datatype cannot store more than 16 digits accurately). Try the following
>> fprintf('%0.20f\n', 1+eps)
1.00000000000000022204
>> fprintf('%0.20f\n', 1+2.5*eps)
1.00000000000000044409

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