Fortran epsilon function equivalent in Julia

user_3952424 0
Viewed 73

I'm starting to learn Julia, and I was wondering if there is an equivalent function in Julia that is doing the same as the epsilon function in Fortran.

In Fortran, the epsilon function of variable x gives the smallest number of the same kind of x that satisfies 1+epsilon(x)>1

I thought the the function eps() in Julia would be something similar, so I tried

eps(typeof(x))

but I got the error:

MethodError: no method matching eps(::Type{Int64})

Is there any other function that resembles the Fortran one that can be used on the different variables of the code?

julia
3 Answers

If you really need eps to work for both Float and Int types, you can overload a method of eps for Int by writing Base.eps(Int) = one(Int). Then your code will work. This is okay for personal projects, but not a good idea for code you intend to share.

user_134950490

As the docstring for eps says:

help?> eps

  eps(::Type{T}) where T<:AbstractFloat
  eps()

eps is only defined for subtypes of AbstractFloat i.e. floating point numbers. It seems that your variable x is an integer variable, as the error message says no method matching eps(::Type{Int64}). It doesn't really make sense to define an eps for integers since the "the smallest number of the same kind of x that satisfies 1 + epsilon(x) > 1" is always going to be 1 for integers.

If you did want to get a 1 of the specific type of integer you have, you can use the one function instead:

julia> x = UInt8(42)
0x2a

julia> one(typeof(x))
0x01
sundar_81270

It seems like what you actually want is

eps(x)

not

eps(typeof(x))

The former is exactly equivalent to your Fortran function.

user_27498650
Related