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Vladimir_M comments on Specification failure - Less Wrong Discussion

5 Post author: cousin_it 04 November 2010 06:56PM

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Comment author: Vladimir_M 05 November 2010 08:07:00PM *  1 point [-]

cousin_it:

No. What do you propose? Use some sort of "comparison tolerance"?

That depends on the concrete numerical application. Typically you'd define some threshold for the difference, and use "abs(x-y)<threshold" instead of "x==y", or some variation on that theme. But exact bit-by-bit equality comparisons of floats practically never make sense, since even very simple arithmetic will likely produce rounding errors, so seeing '==' between floats almost always means that something nonsensical is going on. (See e.g. here for some elaboration.)

These issues with limited floating point precision make numerical programming extremely tricky. You have a whole alternative set of rules for arithmetic, very different from those you normally follow on paper.