When programming before, I sometimes get problem like: a=3.1415926 b=3.1415926 a==b it output false, why? check it out and found b is actually 3.1415926000000001 something like that. so I always have to replace a==b with something like abs(a-b)<10e-10 I noticed Julia has many builtin functions…

[image] PSA: floating-point arithmetic Offtopic Sometimes people are surprised by the results of floating-point calculations such as julia> 5/6 0.8333333333333334 # shouldn't the last digit be 3? julia> 2.6 - 0.7 - 1.9 2.2204460492503…

[image] LarkyJulia: so I always have to replace a==b with something like abs(a-b)<10e-10 See e.g. Comparing Floating Point Numbers, 2012 Edition | Random ASCII – tech blog of Bruce Dawson if you want to read more about floating point comparisons.

[image] LarkyJulia: a=3.1415926 b=3.1415926 a==b Also, this should never be the case in any languages. It’s possible that some don’t show enough digits but none of them should generate different results from the same assignment.

Wow, that’s good reading. Thanks!

Thanks, looks like you guys all suggesting this in Julia to judge if two floats are equal?: abs(a-b)<n*eps(float), with n an appropriate small number .

Not really. Best practice is to think about the context and then use the relevant comparison. Eg even == can be the best choice for unit testing a simple calculation constructed to be exact. See eg isapprox, which has two relevant parameters and is generally a reasonable solution. Also, for the re…

Not really. FWIW, you need to define you problem first. If your problem is having numbers that prints the same compares equal, then that’s already the case in julia. If your problem is to have numbers that prints the same in certain other languages compares equal, well, you need to figure out how…

[image] Tamas_Papp: 3.1415926000000001 == 3.1415926 Wow, I didn’t even try that!!! :grin:That happened to be 1e-16 smaller than eps(Float64)

I find this particularly painful in matrices julia> A = [ 1.0 2.0; 3.0 4.0 ]; invA = inv(A) 2×2 Array{Float64,2}: -2.0 1.0 1.5 -0.5 julia> println(invA) [-1.9999999999999996 0.9999999999999998; 1.4999999999999998 -0.4999999999999999] julia> B=(x->round(x,digits=14)).(invA) 2×2 Array{Float64…

Float representation of the same number may not be equal?

General Usage

Tamas_Papp November 19, 2019, 1:05pm 2

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Float representation of the same number may not be equal?

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